What was the most significant factor in the outbreak of war in 1914

What was the most significant factor in the outbreak of war in 1914?
In 1914 war broke out between many countries in Europe. This happened due to many affecting factors. I am going to be evaluating and recognising the key factors and attempting to identify the most significant cause.

Many historians around the world believe that World War I was inevitable. All the major countries involved in the war believed that they had were superior in comparison to everyone else. This lead to national overconfidence in which everyone expected to win the upcoming, predicted war and there seemed to be more reasons to have a war in comparison than to not. Each country was determined to prove it was greater, stronger and most powerful.