This is an astonishingly complex topic with a vast array of interacting trends, issues and movements. To list some topics that some consider relevant: German and Italian unification, Anglo-German naval race, Pan-slavism, Ottoman Decline, Anglo-French rapprochement, French revanchism regarding Germany, Kaiser Wilhelm himself,Austin-Hungarian expanision in the Balkans, Austria-Hungarian ethnic tensions, Imperialism in general, German expansionism. Consider again that these topics have complex historiographies all of their own and they all interact in multiple ways.

German Unification is a good starting point to get a grasp of late 19th century European history perhaps.