how did the decline of the ottoman empire contribute to world war 1?

Answer 1

De-stabilized the Balcan states, while at the same time freed up Austria-Hungary's military resources.

Answer 2

If the Ottoman empire had remained strong and in control of the Balkans through the 19th century, nationalists in that region would have had few reasons to be hostile to Austria-Hungary, let alone to assassinate the heir to the A-H imperial throne. Their anger and their desire for complete national independence would have been focused almost exclusively against the Ottomans. In 1914, the Ottomans were not part of the Triple Alliance (or any other alliance grouping). Therefore, even if some prominent Ottoman leader had been assassinated by a Serbian nationalist (or any other Balkan brand of nationalist), the action would probably not have led to a general war.

I say "probably not have led to a general war" because Ottoman repression of a Serbian terrorist action could still have brought on a Russian reaction (protecting fellow Slavs and co-religionists); and a Russian military reaction could still have drawn in Austria-Hungary to protect its perceived "influence" in the Balkans. So the machineries of alliance and mabilization could still have gone to work. But not necessarily.

But, of course, the Ottoman empire did not remain strong and in control of the Balkans through the 19th century. Instead, its decline accelerrated. In 1878 Serbia and Rumania won their independence; in 1908, Bulgaria became independent, and A-H nibbled off Bosnia-Herzegovina; in 1912-13, following the 2nd Balkan War, Macedonia and Albania declared independence. The Ottomans had lost their grip on the entire Balkan region by 1914. The Balkans had become a seething, bubbling pot of minor national-states, all ambitiously acquisitive, all locked in ancient mutual hatreds, and all determined to resist domination by either Austria-Hungary or Russia (or anyone else).

The danger posed by Balkan nationalisms in the wake of the Ottoman collapse in the region was foreseen by at least some European statesmen. Bismarck, when asked what might provoke the next war, responded: "Some damned foolish thing in the Balkans."

Answer 3

http://encarta.msn.com/encyclopedia_761553949/Ottoman_Empire.html