It didn't expand the war so much as it lit the fuse that began the actual shooting war.
France
I believe it's Blitzkrieg.
the german invasion of Poland
The invasion of Poland by Germany in Europe in 1939 caused the start of World War II. It was the line drawn in the sand.
Hitlers invasion of russia took place on June 22,1941 during the second world war.
Poland
Britain and it's commonwealth countries (Canada, Australia, New Zealand, etc) declared war on Nazi Germany on September 1st, 1939, when they invaded Poland.
France
Poland
The 1939 invasion of Poland caused Britain to declare war on Germany, which started WWII.
I believe it's Blitzkrieg.
Your teacher probably wants the answer Poland, since it was the German invasion of Poland which led directly to the outbreak of WWII. In fact there had been several German annexations before this (in the 'Sudetenland', and in Austria) which had caused some local fighting. But it was invading Poland which started the big shooting-match.
Germany's invasion of Poland.
The invasion of Poland.
invasion of poland
the event was when Germany invaded Poland. when Britain and France found out they declare war on Germany.
the german invasion of Poland