Abraham Lincoln ended his law career when

O the Kansas-Nebraska Act passed.

O the Republican Party dissolved.

O the Mexican-American War began

O the Democratic Party formed.

C, when the Mexican-American war began.

Explanation:

After doing a simple google search, I learned that Abraham Lincoln ended his law career in 1843. Then I googled "what happened in 1843" and this came up from Wikipedia: April-June. April 30-May 16 - Naval Battle of Campeche: Naval Battle between the Mexican Navy versus the Texas Navy and the Yucatán Navy. The battle features the most advanced warships of its day. May 7 - Nakahama Manjirō lands in New Bedford, Massachusetts, the first known Japanese in the United States."

The answer is c my friend