They used sonar to detect german submarines. sonar reflects of underwater sound waves
Evidence would be that child labor laws were put in place since children would work long hours for little pay in very very rough conditions.
There were a number of events, such as the bombing of the USS Cole, that led up to the US War on Terrorism but the major event was the hijacking of airplanes and the flying of those airplanes into the World Trade Center and the Pentagon on Sept. 11, 2001.
<span>People used slavery with the excuse that they needed someone to tend to their crops for them, as well as their house, etc. It's never justified, however, and I'm curious as to what the heck was crossing their minds when they brought the first slaves over, even though America is known as the land of the free, but you know, whatever</span>
by making more than one pieces of work