German actions bringing European tension to the breaking point included:

Question

German involvement in the Balkans
German friction with Serbia
a proposed German railroad
the build-up of the German navy

Answer 1

the aggressive German foreign policy
the increasing militarization of Germany
German support for Austria-Hungary in the July Crisis of 1914
the German invasion of Belgium in violation of its neutral status
the sinking of the British passenger ship Lusitania by a German U-boat in 1915
the unrestricted submarine warfare campaign by Germany during World War I
the Zimmerman Telegram, in which Germany proposed an alliance with Mexico against the United States.