The responsibility for the outbreak of World War I is maybe one of the most discussed questions in modern history, so you will find scholars arguing for and against every side of the conflict. In most works however, Austro-Hungary is widely considered to hold little responsibility for several reasons:

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1. The investigation of Franz Ferdinand's death and the following military intervention are considered justified by the standards of the time.
2. However, Austro-Hungary would have refrained from military action against a Russian ally (Serbia), had it not been sure of German support. By assuring them of this support, Germany encouraged military intervention, knowing that Russia would most likely react by declaring war, engaging France and Britain. Thus, the German assurances were the crucial factor that escalated a regional intervention into a European, and later world wide, war.
3. The long-term developments leading up to the July Crisis are often seen in Germany's history under Wilhelm II. Germany's late nation building, the destruction of Bismarck's alliances, the arms race against Great Britain, the wish for world renown, colonial conflicts etc. destabilized the European power equilibrium. Meanwhile, Germany grew to the defining industrial power on the continent, concerning neighboring powers and leading to the notion of an inevitable war. During this time, Austro-Hungary was mostly occupied with keeping up its unification in times of emerging nationalism and a deep divide between the Austrian and the Hungarian part of the empire. Several crises and wars on the Balkan weakened Austro-Hungarian military and political power.
4. The biggest point of debate is still, to what extent German politicians expected and/or wanted a full scale war when they assured Austro-Hungary of their support. For Austro-Hungary itself, the answer seems clear: They wanted to "teach Serbia a lesson" and use the Serbian Crisis as an occasion to prove their power, but they most likely did not see the risk of an escalation.

The reasons for World War II are, of course, not up for debate. In "Mein Kampf", Hitler explained in detail how a European land war was the only way for Germany to survive, how one must set up the economy, the school system, the propaganda in preparation of war, keep Italy and Austria as allies, attack and defeat France first, then move on to Russia, while keeping Britain out of it all.

Austria, according to national-socialist ideology, should never have been an independent state, as it belonged to the German Kulturkreis. Thus, in 1938, it was annexed in the so-called "Anschluss". From then on, it was part of the German Reich.

So of course there were Austrian Nazi politicians and perpetrators. But the responsibility of the Austria as a state is indeed debated over today. Even though many Austrians had supported Hitler and welcomed the "Anschluss", Austria proclaimed to be the "first victim" of Nazi Germany for decades, denying for example all payments of compensation. It was not until 1993 that the Austrian chancellor accepted responsibility and apologized to the State of Israel. From what I know, the question of national responsibility is still quite sensitive in Austria. But considering their integration into the German Reich, it is very complicated to blame Austria as a state for World War II.