Why did Germans take alsace and lorraine in World War 1?

Many reasons. First off, it depends what time period we are talking about. Both countries, quiet rightly wanted the land as they both wanted to expand; Alsace-Lorraine was in between them so both felt like it was a possible addition. Also, Alsace-Lorraine had a lot of German speaking people in it and was therefor strategically good for Germany.

If we are talking 20th century, than France wanted it back as it was originally French until 1871 Franco-Prussian war, where Germany got hold of it. Ever since this, France wanted the land back (and it did get it back after the first World War, in 1919, thanks to the terms of the Treaty of Versailles), however, obviously, Germany did not want to give it back.

After this, Germany wanted revenge and so it invaded France again in 1940.

Hope this helps. :P