From most of my research, English common law developed out of ancient Germanic tribal law. Why was England the only country that kept this practice? Were there other countries that had this practice, but switched over to civil law? If so, how did they differ from English common law, or were the practices largely the same?
It was not a question of simply keeping the old Germanic tribal law or moving to something else. The common law in England emerged from the intersection of local expressions of Anglo-Saxon law (with its germanic roots), on the one hand, with the Norman French law, on the other, in the 11th and 12th centuries and following. They were trying to bring together these two systems along with some kind of local, intuitive sense of fairness.