Many countries in Europe were ready to attack each other at any point in time with the amount of struggle between these nations in the years before the war. As most of the struggle between these nations is hopefully gone after 2 huge wars, I would hope something like this would not happen for a very long time.
I think there is no question that WWI was caused by national rivalries. There were certainly other factors such as economic and political, but nationalism above all paved the way for a world war. This is usually the case when conflict happens for no apparent reason and is a great threat to peace.
Yes, I think that the events that led to the first world war had building up for decades between the countries, and was not an event that just suddenly occurred over one thing. I think that the first world war had building up between the countries for a very long time.
I think that decades of tension between European rivals help cause some of the reasons for World War I to start, but it was not the main reason. The tension would obviously be a factor because they are walking on eggshells and ready to crack and the slight misunderstanding, but it probably wasn't the only reason either.
Slavs, germanic peoples, and European Jews had many tensions over the years between each other. The idea that Franz Ferdinand being shot in Slavic territory was the official start of WWI downplays the tensions these groups had for each other for hundreds of years. The Great War would have eventually happened even without this action.