Warfare is simply politics that have been publicized.
Another reason that Austria attacked Serbia was because of inside issues. The Austria-Hungary Alliance wanted more people under it as to help with diplomatic problems (eg: voting) and when they saw Serbia, they saw a nation with a lot of Slavs. They hoped that the Slavs would join the alliance, being of Slavic descent themselves (nationalism). This was reflected when the Austrians attempted to incite a Slavic revolt in Serbia.
Germany gave backing to Austria because it that that the Austrians would deal with the Russians (at least for a "good" while), while Austria attacked Serbia because they though Germany would help them deal with any angry Russians. Also, the German's underestimated the time it would take Russia to mobilize, despite how slow the Russians turned out to be.
One reason the Germans made a navy was because they already had the strongest land-based army, and were hoping to recieve gains with more control of affairs away from home. (Despite how Britain had much of Asia along with sea dominance. Also, the British had roughly more than twice the tonnage of Germany prior to WW I, too, so it was rashy of Germany.)
"Proof" that France wanted war: They lost Alsace etc. in the Franco-Prusso war in the late 1800s. (Mentioned) Also, they wanted war so badly that there was only one influencial member in the French government that hoped for pacifism, and he was assasinated for wanting peace. (By a frenchman.)
Some Germans thought that the war might go on for a year or a few, as warfare had changed greatly. Still, the supposing leaders on all sides couldn't stop the possibility of a bloody war. One example of how little understanding they had was that the French attacked the Germans in bright and colorful uniforms rather than more practical camo. Also, belief that war would end quickly helped increase morale and enlistment.