Responsibility can be divided among many individuals, groups, countries, and empires, but the first shots were fired by a lone Serbian assassin named Gavrilo Princip.
nazism and conquering
No, the assassination of Archduke Ferdinand started the war.
No, Hitler didn't have much to do with starting World War 1, Word War 2 is another matter though.
The Balkans were called the "Powder Keg of Europe" because they were responsible for World War I starting.
One of their members, Gavrilo Princip, assassinated the Archduke Franz Ferdinand of Austria Hungary, starting the war.
Germany
No, Britain wasn't responsible. Austria Hungary was.
Germany
World War 1 was started after the sinking of the Lusitania.
Probably artillery; it was responsible for many of the deaths in World War 1.
imperialism
Everyone in a way but mostly it was germany