The military actions of what country are described above?
broke terms of versailles treaty by building up its military and land-stealing.
seized austria in 1938, czechoslovakia in 1939.
invaded poland in september 1939, setting off world war ii.
germany
italy
russia
great britain

This is Germany!

Germany invaded Austria in 1938, with a partial acceptance of the Austrians because they believed that the two countries should merge based on their cultural similarities.

It also later invaded Czekoslovakia in 1939 and later in the year Poland and started World War II.

The military action which is being described in the above paragraph would be one the actions from Germany. 

They did exactly as described - Germany brok the treaty of Versailles and started building up a military and started land-stealing as well. Both things were precursors to the second World War.