Germany used or submarines to prevent britain from blockading supplies.

in 1862, president lincoln's emancipation proclamation opened the door for african americans to enlist in the union army. although many had wanted to join the war effort earlier, they were prohibited from enlisting by a federal law dating back to 1792.

explanation:

"germany's geographic location was an advantage when it was on the offensive in the war because it was situated next to an extremely wide river, the rhine, which was difficult for the allies to cross."