Why Russians call Germans Немка/Немец

A few centuries ago the slavic and the germanic tribes lived in Europe as rivals. The germanic tribes lived in the middle west of Europe, the slavic tribes in the middle east. Each tribe spoke a different language, but all slavic languages were close to each other, so that they were able to communicate. Same with the germanic languages. But when a germanic and a slavic tribe met, they were not able to talk to each other. Since this time the slavic tribes started to call Germanics as people who are not able to talk, because they could not understand them. Now the Russians call germans немец/немка. Also many other slavic countries call them in a similar way; Bosnians, Bulgarians, Croatians, Romanians, Serbs, Slovaks, Slovenians, Czechs, Ukranians and Hungarians.