Which is the correct use of the word “emerged”?
west african kingdoms emerged to form one union.
trade emerged as a main source of income.
gold emerged from one merchant to another.
which merchant will best emerge the wealth?

I believe the answer is: Trade emerged as a main source of income.

The word 'emerge' means something that start to become prominent or dominant as the time goes by.

During its early introduction, trade was not really popular since many people still choose to take care of their own agricultural field as their main source income. It took hundred of years before trade finally acknowledge as something profitable

when world war i broke out across europe in 1914, president woodrow wilson proclaimed the united states would remain neutral, and many americans supported this policy of nonintervention. however, public opinion about neutrality started to change after the sinking of the british ocean liner lusitania by a german u-boat in 1915; almost 2,000 people perished, including 128 americans. along with news of the zimmerman telegram threatening an alliance between germany and mexico, wilson asked congress for a declaration of war against germany. the u.s. officially entered the conflict on april 6, 1917.