What did the border states have in common with the
Confederacy?

They were Slave states

All of these states had strong support for both the Confederacy and the Union.  

Explanation:

Keeping control of the border states played an important role in the victory for the Union. These states gave the Union the advantage in troops, factories, and money.

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.

north atlantic treaty organization.