Palo Alto, 8 May 1846. Conditionshad been steadily worsening along the Rio Grande. The United States claimedthe Rio Grande as the international border while the Mexican Government claimedthe Nueces was the proper border. Early in 1846, General Zachary Taylor builta fort on the Rio Grande opposite the Mexican town of Matamoros. In April, theMexicans countered by sending a force of about 1600 cavalrymen across the RioGrande where, on 25 April, they overwhelmed a force of 60 dragoons under CaptainS. B. Thornton.

Mexican forces at Matamoros steadilygrew stronger in April. By the end of the month General Taylor had become concernedabout his lines of communication with his lightly held main base at Point Isabel,near the mouth of the Rio Grande. Therefore, on 1 May Taylor moved the bulkof his army to Point Isabel, leaving a small detachment of artillery and infantryunder Maj. Jacob Brown at the fort opposite Matamoros. The Mexicans soon placedthis fort (later named Fort Brown) under heavy attack. On 7 May Taylor movedto the rescue with about 2,300 men. On the morning of 8 May, when little morethan half way to the fort, the Americana came face to face with the enemy, aforce numbering perhaps as many as 6,000 men, commanded by Gen. Mariano Arista.Its right flank rested on an elevation known as Palo Alto (after which the engagementwas named). Taylor moved unhesitatingly into battle, using his artillery tocover the deployment of the infantry. The engagement continued until nightfall,when the Mexicans withdrew. Effective use of artillery fire was largely responsiblefor the American victory. American losses were 9 killed and 47 wounded. TheMexicans suffered more than 700 casualties, including about 320 deaths.

Resaca de la Palma, 9 May 1846.The next morning Taylor, continuing his advance, found the Mexicans a few milesdown the road, where they had taken up a strong defensive position in a dryriver bed known as the Resaca de la Palma. In this second successive day ofbattle the infantry conducted most of the action, although the dragoons playedan important part in knocking out the enemy artillery. Eventually the infantryturned the enemy's left flank, and the Mexican line broke and fled. The routbecame a race for the Rio Grande which the Mexicans won, but many were drownedwhile attempting to cross the river. Taylor's losses were 33 killed and 89 wounded.Arista's official report listed 160 Mexicans killed, 228 wounded, and 159 missing,but Americas estimated that the Mexicans had suffered well over a thousand casualties.

Taylor had to wait until 18 Mayfor boats to move his army across the Rio Grande. When the Americans finallymoved into Matamoros, they found that the Mexican force had disappeared intothe interior. The next objective was Monterey, but the direct overland routefrom Matamoros lacked water and forage; Taylor therefore waited until Augustfor the arrival of steamboats, with which he moved his army 130 miles upriverto Camargo. Meanwhile thousands of volunteers had poured into Matamoros, butdisease and various security and logistic factors limited Taylor to a forceof little more than 6,000 men for the Monterey campaign.

Monterey, 21 Sentember 1846.Taylor's forces left Camargo at the end of August and launched an attack onMonterey on 21 September 1846. The city was defended by a force of from 7,300to 9,000 Mexican troops under the command of Gen. Pedro de Ampudia. After threedays of hard fighting the Americans drove the enemy from the streets to thecentral plaza. On 24 September Ampudia offered to surrender the city on thecondition that his troops be allowed to withdraw unimpeded and that aneight-week armistice go into effect. Taylor, believing that his mission wassimply to hold northern Mexico, accepted the terms and the Mexican troops evacuatedthe city the following day. Ampudia reported that his army had suffered 367casualties in the three-day fight. Taylor reported his losses as being 120 killedand 368 wounded. Both reports were probably underestimates.

Taylor was severely criticized inWashington for agreeing to the Mexican terms, and the Administration promptlyrepudiated the armistice, which had almost expired by the time the news reachedMonterey.

Meanwhile, in keeping with the strategicplan, the other two prongs of advance into northern Mexico had been put in motion.On 5 June 1846, Brig. Gen. John E. Wool had left San Antonio with his "Armyof the Center," a force of some 2,000 men. His original objective was Chihuahua,but en route it was changed to Parras. Wool, encountering no opposition, arrivedat Parras on 5 December; his force then became part of Taylor's command. Thethird prong, Col. (later Maj. Gen.) Stephen W. Kearny's "Army of the West,"a force of about 1,660 men, left Fort Leavenworth early in June 1846 and enteredSanta Fe unopposed on 18 August. From there Kearny left for California on 25September with about 300 dragoons. En route he met a party, led by Kit Carson,bringing news from the west coast that a naval squadron under Commodore J. D.Sloat, with the questionable help of volunteers under Capt. John C. Fremont,had won peaceful possession of California in July, although some oppositionremained. Kearny seat back 200 of his men and pushed on with the rest, arrivingat San Diego on 12 December after having fought a sharp engagement on 6 Decemberwith a larger force of Californians at San Pasqual. At San Diego Kearny joinedCommodore Robert F. Stockton, who had replaced Sloat, and their combined forceof some 600 men, after same minor skirmishing, occupied Los Angeles on 10 January1847. Three days later the last remaining Californian opposition capitulatedto the volunteer force commanded by Fremont.

Meanwhile, in mid-November of 1846,Taylor had sent one of his divisions to occupy the city of Saltillo. Anotherdetachment occupied Victoria, a provincial capital between Monterey and theport or Tampico, which latter had been occupied by an American naval force underComdr. David Conner on 15 November 1846. Thus, by the end of 1846, a very largepart of northern Mexico had come under American control.

A plan was adopted late in 1846to strike at Mexico City by way of Vera Cruz. In preparation for this expeditionMaj. Gen. Wintield Scott, Commanding General or the Army, detached about 8,000men from Taylor 'a command early in 1847, ordering the troops to Gulf portsto wait sea transportation. Taylor was left with some 4,800 men, practicallyall volunteers, most or whom he concentrated in a camp south of Saltillo.

Buena Vista, 22 - 23 February1847. Gen. Santa Anna, President of Mexico, had meanwhile taken the fieldpersonally and assembled an army at Son Luia Potosi. Learning of the weaknessof the forces near Saltillo, Santa Anna moved with about 15,000 men tothe attack in February 1847. Taylor hastily redeployed his force at Buena Vista,where the terrain offered better possibilities for defense. Santa Anna usedFrench tactics at Buena Vista, attempting to overwhelm American positions withdense columns of men. Massed tires of infantry and artillery proved effectiveagainst the attacking columns, and, after two days of the most severe fightingof the war, Santa Anna withdrew his dispirited army to San Luis Potosi, havinglost from 1,500 to 2,000 men killed and wounded. The Americans, too exhaustedto pursue, had lost 264 killed, 450 wounded, and 26 missing.

Vera Cruz, 9 - 29 March 1847.Scott's army, numbering 13,660 men, rendezvoused at Lobos Island late in February1847 and on 2 March sailed for Vera Cruz, convoyed by a naval force under CommodoreMatthew C. Perry. Landing operations near Vera Cruz began on 9 March. This firstmayor amphibious landing by the U.S. Army was unopposed, the Mexican commandantegeneral, Juan Morales, having decided to keep his force of only 4,300 men behindthe city's walls. In order to save lives, Scott chose to take Vera Cruz by seigerather than by assault. The city capitulated on 27 March 1847 after undergoinga demoralizing bombardment. The Americans lost 19 killed and 63 wounded. TheMexican military suffered only about 80 casualties.

Cerro Gordo, 17 April 1847.Scott began his advance toward Mexico City on 8 April 1847. The first resistanceencountered was near the hamlet of Cerro Gordo where Santa Anna had stronglyentrenched an army of about 12,000 men in mountain passes through which theroad ran to Jalapa. Scott quickly won the battle with a flanking movement thatcut off the enemy escape route, and the Mexicans surrendered in droves. From1,000 to 1,200 casualties were suffered by the Mexicans, and Scott eventuallyreleased on parole the 3,000 who had been taken prisoners. Santa Anna and theremnants of his army fled into the mountains. American losses were 64 killedand 353 wounded.

Scott quickly pushed on to Jalapa,but was forced to wait there for supplies and reinforcements. After some weekshe advanced cautiously to Pueblo. Wounds and sickness put 3,200 men in the hospital,and the departure for home of about 3,700 volunteers (seven regiments) whoseenlistments had expired left Scott with only 5,820 effective enlisted men atthe end of May 1847. Scott stayed at Puebla until the beginning of August, awaitingreinforcement and the outcome of peace negotiations which were being conductedby Nicholas P. Trist, a State Department official who had accompanied the expedition.

The negotiations having failed,Scott boldly struck out for Mexico City on 7 August, abandoning his line ofcommunications to the coast. By this time reinforcements had brought his armyto a strength of nearly 10,000 men. Santa Anna had disposed his army in andaround Mexico City, strongly fortifying the many natural obstacles that layin the way of the Americans.

Contreras, 18 - 20 August 1847.Scott first encountered stiff resistance at Contreras where the Mexicans werefinally put to flight after suffering an estimated 700 casualties and the lossof 800 prisoners.

Churubusco, 20 August 1847.Santa Anna promptly made another stand on Churubusco where he suffered a disastrousdefeat in which his total losses for the day-killed, wounded, and especiallydeserters-were probably as high as 10,000. Scott estimated the Mexican lossesat 4,297 killed and wounded, and he took 2,637 prisoners. Of 8,497 Americansengaged in the almost continuous battles of Contreras and Churubusco, 131 werekilled, 865 wounded, and about 40 missing.

Scott proposed an armistice to discusspeace terms. Santa Anna quickly agreed; but after two weeks of fruitless negotiationsit became apparent that the Mexicans were using the armistice merely for a breathingspell. On 6 September Scott broke off discussions and prepared to assault thecapital. To do so, it was necessary to take the citadel of Chapultepec, a massivestone fortress on top of a hill about a mile outside the city proper. DefendingMexico City were from 18,000 to 20,000 troops, and the Mexicans were confidentof victory, since it was known that Scott had barely 8,000 men and was far fromhis base of supply.

Molino del Rey, 8 September 1847.On 8 September 1847, the Americans launched an assault on Molino del Rey, themost important outwork of Chapultepec. It was taken after a bloody fight, inwhich the Mexicans suffered an estimated 2,000 casualties and lost 700 as prisoners,while perhaps as many as 2,000 deserted. The small American force had sustainedcomparatively serious losses-124 killed and 582 wounded-but they doggedly continuedtheir attack on Chapultepec, which finally fell on 13 September 1847.American losses were 138 killed and 673 wounded during the siege of the fortress.Mexican losses in killed, wounded, and captured totaled about 1,800. The fallof the citadel brought Mexican resistance practically to an end. Authoritiesin Mexico City sent out a white flag on 14 September 1847. Santa Anna abdicatedthe Presidency, and the last remnant of his army, about 1,500 volunteers, wascompletely defeated a few days later while attempting to capture an Americansupply train.

On 2 February 1848, the Treatyof Guadalupe Hidalgo was signed, ratified in the U.S. Senate on 10 March 1848,by the Mexican Congress in May, and on 1 August 1848 the last American soldierdeparted for home.