Why did the Thirty Years war begin?

The 30 years war bean because of the spreading protestant reformation. Many princes in Germany felt under control by charles V, Holy Roman Emperor, and so by becoming protestant they thought that they would have more power. Other countries, such as the French, sought to curb the power of the Holy Roman Empire and the Hapsburgs, even though they were a Catholic Country. Meanwhile, the Hapsburgs wanted to extend their power through the war. So basically, it was a war to gain land and power, but "religious" motivation was the mask of that.