The Mexican-American War began when the U.S. Congress — after several border skirmishes between the two countries — declared war on Mexico on May 13 of what year?

The Mexican-American War began when the U.S. Congress — after several border skirmishes between the two countries — declared war on Mexico on May 13 of what year?

1812
1836
1846
1851
1896

The correct answer is 1846.