To me, the main significance of this event is that it marks the first real attempt by Nazi Germany to expand its borders. This expansion would lead to the start of WWII.
After Germany took over Austria, it went on to demand part and then all of Czechoslovakia. After that, it thought it could take Poland with impunity. It was this invasion that led to the war.
The actual annexation of Austria had little impact outside of Austria. I think its only real importance is that it was the start of a series of moves that led to war.