What was one of the events that led to u. s. involvement in wwi? u. s. troops were captured after they were sent on a peace seeking mission. germany sunk the lusitania and other american ships. germany invaded waters too close to the united states. the united states sunk german u-boats, aggravating tensions between the two countries. why did germany sign an armistice in 1918? germany's allies collapsed and retreated. the armistice was a temporary halt to the war and germany needed to refresh troops. turkey was the only ally left and that wasn't enough to fight. germany wanted to allow the central powers time to regroup.