Unrestricted submarine warfare and the Zimmerman telegram brought which nation into world war 1

Which is the best example of a primary source ducument useful in the study of history ?

The battle of sabine pass is important because? a) it was a stalemate between union and confederate armies. b) it resulted in the largest confederate casualty in the war. c) it marks the failed attempt of the union army to invade the confederate state of texas. d) it was won by the union soldiers and marked a turning point in the western front of the war.

Over time, who did the nature of slavery change in america