Advancement in aviation. History's first naval wars fought entirely by airplanes at the Battle of the Coral Sea; history's first clash of aircraft carriers.
XXth century: Balkanic war, World War I, World War II and many other wars during a long unfortunate history.
The Strategy used during both world wars is Total War
Switzerland was neutral during both World Wars.
?? WW2 or World WAR 2 was a war.
The men were fighting in the wars.
1933 between the wars
Spain was neutral during both World Wars.
There were many soldiers at the end of the World War 1 during the end of the world war.
The United States fought as a whole, and not particular to individual states.
WW1.... You answered that for yourself.
The significant civil war that happened just before WW II was the Spanish Civil War.
the cold wars