What action started the mexican american war in 1846?
a. president polk ordered us troops to invade mexico and capture vera cruz and mexico city.
b. sam houston refused to return mexican land in texas that had been turned over by santa anna.
c. a. president tyler sent troops into mexico and demanding the california territory provoking war.
d. us troops, following orders from president polk, claimed an area of disputed land for the united states which caused an attack by mexico in retaliation

The answer is:

D. US troops, following orders from President Polk, claimed an area of disputed land for the United States which caused an attack by Mexico in retaliation

Explanation:

The major cause of the war was actually  the annexation of Texas by the US in 1845. Among tensions, skirmishes and a failed diplomatic mission, president Polk ordered American troops commanded by Gen. Zachary Taylor to occupy the disputed zone between Río Nueces and Río Grande (Río Bravo for Mexicans) in January 1846. Taylor´s men were attacked by Mexican troops in April killing or injuring 16 of them. Polk claimed Mexican soldiers had attacked US troops and "shed American blood upon American soil." He requested a declaration of war. Congress overwhelmingly voted to declare war on Mexico on May 13, 1846.

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