Mexican–American War : 米墨戦争

The Mexican–American War, also known as the Mexican War in the United States and in Mexico as the American intervention in Mexico, was an armed conflict between the United States of America and the United Mexican States (Mexico) from 1846 to 1848. It followed in the wake of the 1845 American annexation of the independent Republic of Texas, which Mexico still considered its northeastern province and a part of its territory after its de facto secession in the 1836 Texas Revolution a decade earlier.

Mexico obtained independence from the Kingdom of Spain and the Spanish Empire with the Treaty of Córdoba in 1821, and briefly experimented with monarchy, becoming a republic in 1824. It was characterized by considerable instability, leaving it ill-prepared for international conflict only two decades later, when war broke out in 1846. In the decades preceding the war, Native American raids in Mexico’s sparsely settled north prompted the Mexican government to sponsor migration from the United States to the Mexican province of Texas to create a buffer. However, the newly named “Texians” revolted against the Mexican government of President/dictator Antonio López de Santa Anna, who had usurped the Mexican Constitution of 1824, in the subsequent 1836 Texas Revolution, creating a republic not recognized by Mexico, which still claimed it as part of its national territory. In 1845, the Texan Republic agreed to an offer of annexation by the U.S. Congress and became the 28th state in the Union on December 29 that year.

In 1845, newly elected U.S. President James K. Polk made a proposition to the Mexican government to purchase the disputed lands between the Nueces River and the Rio Grande river further south. When that offer was rejected, President Polk moved U.S. troops commanded by Major General Zachary Taylor further south into the disputed territory. Mexican forces attacked an American Army outpost (“Thornton Affair”) in the occupied territory, killing 12 U.S. soldiers and capturing 52. These same Mexican troops later laid siege to an American fort along the Rio Grande. Polk cited this attack as an invasion of U.S. territory and requested that the Congress declare war.

U.S. forces quickly occupied the capital town of Santa Fe de Nuevo México along the upper Rio Grande and the Pacific coast territory province of Alta California (Upper California). They then invaded to the south into parts of central Mexico (modern-day northeastern Mexico and northwest Mexico). Meanwhile, the Pacific Squadron of the United States Navy conducted a blockade and took control of several garrisons on the Pacific coast farther south in lower Baja California Territory. The U.S. Army, under the command of Major General Winfield Scott, after several fierce battles of stiff resistance from the Mexican Army outside of the capital, Mexico City, eventually captured the city, having marched west from the port of Veracruz, where the Americans staged their first amphibious landing on the Gulf of Mexico coast.

The 1848 Treaty of Guadalupe Hidalgo, forced onto the remnant Mexican government, ended the war and specified its major consequence, the Mexican Cession of the northern territories of Alta California and Santa Fe de Nuevo México to the United States. The U.S. agreed to pay $15 million compensation for the physical damage of the war. In addition, the United States assumed $3.25 million of debt already owed earlier by the Mexican government to U.S. citizens. Mexico acknowledged the loss of their province, later the Republic of Texas (and now the State of Texas), and thereafter cited and acknowledged the Rio Grande as its future northern national border with the United States. Mexico had lost over one-third of its original territory from its 1821 independence.

The territorial expansion of the United States toward the Pacific coast had been the goal of Polk, the leader of the Democratic Party. At first, the war was highly controversial in the United States, with the Whig Party, anti-imperialists, and anti-slavery elements strongly opposing. Critics in the United States pointed to the heavy casualties suffered by U.S. forces compared to earlier American wars, and the conflict’s high monetary cost. The war intensified the debate over slavery in the United States, contributing to bitter debates that culminated in the American Civil War (1861–1865).

In Mexico, the war came in the middle of continued domestic political turmoil, which increased into chaos during the conflict. The military defeat and loss of territory was a disastrous blow, causing Mexico to enter “a period of self-examination… as its leaders sought to identify and address the reasons that had led to such a debacle.” In the immediate aftermath of the war, some prominent Mexicans wrote that the war had resulted in “the state of degradation and ruin” in Mexico, further claiming, for “the true origin of the war, it is sufficient to say that the insatiable ambition of the United States, favored by our weakness, caused it.” The shift in the Mexico-U.S. border left many Mexican citizens separated from their national government. For the indigenous peoples who had never accepted Spanish or Mexican rule, the change in border meant conflicts with a new outside power.


アメリカ合衆国ではメキシコ戦争として知られている。メキシコでは、アメリカ合衆国のメキシコ侵略(U.S. American Invasion of Mexico)、米国の対メキシコ戦争(United States War Against Mexico)、北部の侵略戦争(War of Northern Aggression)として知られている(なお最後の名称は、アメリカ南部では南北戦争を指すことが多い)。








テキサスを併合したアメリカは、メキシコとの国境をリオグランデ川(Rio Grande)以北としていた。一方メキシコは同様にリオグランデ川の北側を流れるヌエセス川(Nueces River)以南としており、両国の主張には相違があった。時のアメリカ大統領ジェームズ・ポークは、アメリカの主張するテキサス州の土地を確保するよう軍に命じた。これを受けたザカリー・テイラー将軍の率いる軍隊は、ヌエセス川を南に超えて、メキシコの非難にもかかわらずブラウン砦(Fort Brown)を築いた。1846年4月24日にメキシコの騎兵隊がアメリカの分遣隊を捕らえたことから戦闘状態となった。パロアルト(Palo Alto)およびレサカ・デ・ラ・パルマ(Resaca De La Palma)での国境衝突および戦闘の後に、連邦議会は5月13日に宣戦を布告。南部出身者と民主党がそれを支持した。一方北部出身者とホイッグ党員は一般に、戦争の宣言に反対した。メキシコは5月23日に宣戦を布告した。




このメキシコ割譲により、メキシコは国土の 1/3 を失った。これによる国民の不満もあり、1864年8月22日には政権が交代し、また中央集権国家のメキシコ合衆国に戻った。不毛の砂漠地帯だったこれらの土地ではあったが、その1年後(1849年)カリフォルニア州サクラメントでゴールドラッシュが起こり、さらに後の20世紀前半には、テキサス州に無尽蔵といわれた油田が発見されて石油ブームが起こることになる。






アメリカ退役軍人協会からのデータによれば、米墨戦争に従軍した最後の生き残りオーエン・トマス・エドガー(Owen Thomas Edgar)は、1929年9月3日に98歳で死去した。



  • Richard H.Berg 【Rough & Ready】,Strategy & Tactics No.212,Decision Games
  • Halls of MONTEZUMA,GMT Games

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