Why did Germany want war with Britain in World War 1?

Answer 1

It didn't, or not just then anyway. What Germany wanted in 1914 was for Britain to stay neutral while Germany crushed France and Russia and so gained full control of Europe. This was of course impossible, since it would have left Britain facing a continent united under the rule of her most dangerous rival, who might then have used Europe's resources to build a navy larger than the British. Hence the British declaration of war on 4 August 1914.

Answer 2

Germany didn't particularly want Britain's empire, they just wanted one in general. In comparison to other countries Germany was a new country. This was because all the parts had come together to form the country. Germany viewed empires as power, and wanted to part of it as Britain and France already has reasonably large empires and colonies. This rise to power by Germany was one of the cause leading to World War 1.