To what country did the Rhineland belong before Germany sent troops there on March 7 1936?

Before Germany sent troops into the Rhineland on March 7, 1936, the Rhineland was part of Germany but had been demilitarized following World War I under the Treaty of Versailles. The region was subject to strict limitations to prevent future German aggression. The remilitarization by Germany was a violation of this treaty and marked a significant turning point in the lead-up to World War II.