Some historians such as Sir Richard J Evans, believed that it was Serbia's fault for escalating the hostility between Austria-Hungary because of their rise in nationalism. However, before the war, Germany had high tensions between Britain, Russia, and France. The French had a grudge with Germany over the Franco-Prussian War in 1871, which resulted in France losing Alsace-Lorraine to Germany. More animosity rose when Germany accused Britain, Russia and France of trying to surround them from the threat of the Triple Entente. In 1914, Britain had the strongest navy, and Germany had the largest land army. This caused naval rivalry between Germany and Britain. With several rivalries and tensions between Germany and the Triple Entente, Germany could easily launch a massive scale war if they decided to go against one of the three countries or any ally of them. Despite that Germany was fully aware of the situation, it decided to support Austria-Hungary's campaign against Serbia.
Germany gave unconditional support to Austria-Hungary by providing the "Carte Blanche," the blank check. This gave Austria-Hungary the power to fully put in use Germany's army and launch a war against Serbia. Although it was Austria-Hungary calling war against Serbia, if it didn't have Germany's army and financial support, it wouldn't had acted so drastically. Austria-Hungary declared war on Serbia because Germany urged them to invade Serbia. Wilhelm II took an aggressive path that broke Bismarck’s plan of peace and balance. Prussian German conservative elites were convinced that a European war would help fulfill German ambitions for colonies and military prestige. Germany was fully aware that if it was to support Austria-Hungary to invade Serbia, France and Russia would be involved in the war as well. They also started wider European hostilities by sending ultimata to Russia and France, and declared war when those ultimata were rejected. Germany pulled Russia and France to war, causing a large scale European war. It then pulled Great Britain and America into this war.
Germany was the main cause in transforming a large scale European war into a worldwide war. Other countries started to involve themselves in the war after Germany's violations of international treaties of each country's sovereignty. After involving France and Russia in the war, Germany invaded Belgium, which was in a neutral position. Belgium was a huge ally to Britain, and both wanted to stay out of the war. Nevertheless, Germany attacked Belgium, and it triggered Great Britain to strike back in retaliation. By pulling in Britain, the scale of the war escalated, and prolonged it even more. The US was also trying to pull back and not be involved in the war, as it was more isolated from international relations. However, Germany at first almost pulled US into the war by sinking its passenger ships and trading ships to Britain. Despite the fact that Germany wouldn't want the US to be involved, they still created the Zimmermann note. The note was a telegram asking Mexico to attack the US, and in return, they'll regain the land they lost to the US. The telegram was intercepted which caused the US to be involved, and several of other allies of the US as well. The war was now a World War.
Through these analysis, we could easily see the consequences of Germany's actions prior and during the war, leading to the first World War. Germany, fully aware of the potential reactions, caused Austria-Hungary to take drastic choices of declaring war on Serbia. Germany had also purposely created tensions with other countries, so when Germany also declared war, other countries joined in. By pulling in the US and Britain, Germany increased the scale of the war into a world war. Countries that were pulled in were mostly because of its tension and ties with Germany. If Germany wasn't involved in the war, it wouldn't have escalated to a massive scale. Germany had the power to halt the descent to disaster, since it had major influence over Austria-Hungary. It could've prevented Austria-Hungary from declaring war if it wasn't for the "blank check" provided to Austria-Hungary. By judging the amount of power Germany had to prevent the war, one could say that Germany had caused several of the events that led to World War I. This is why Germany deserved the most blame for the cause of World War I.