From WWI to WWII:

We all know these two wars more or less. Some of us know it from history class and some from documentaries, movies, and novels, etc. After establishing the congress of Vienna, Europe was in peace in general from 1815 to 1914. For a few years, it was disturbed by the Crimean war but it was far from mainland Europe. It was a balance of power because Russia was unstoppable and the Ottoman Empire was in a steady decline. So from one perspective, it was good for the balance of power. The German victory over France in  Franco-Prussian War 1870–1871 disturb the Balance of Power. The rise of industrious and united Germany gain tremendous power. The defeat of 1870-71 was a humiliation for France as well as the loss of  Alsace-Lorraine. Avenging the defeat and recovery of  Alsace-Lorraine was the French policy for the next forty years. This was very heavy for France to go to war with Germany. The German chancellor  Otto von Bismarck was well aware of this so he was trying to keep France separate. For this, he formed an alliance called the League of the Three Emperors, which consisted of Austria, Germany, and Russia.

In 1877–1878 Russia defeated Ottoman Empire and this increase her influence over the Balkans. Austria becomes anxious about this victory of Russia. So they dissolved this alliance and formed Dual Alliance in 1879. Later on, Italy Joined Dual Alliance which becomes Triple Alliance. Each member of the Alliance has its own interest in it, Germany wanted to keep France isolated. Britain and France tried to keep Russia on their sides but Bismarck make a secret treaty (Reinsurance Treaty) to make sure that Russia remain neutral if Germany is attacked by France.

In 1890 Bismarck was retired by the new Emperor  Wilhelm II. Germany did not renew the Reinsurance Treaty with Russia. France was waiting for such an opportunity. In 1894 France and Russia signed the  Franco-Russian Alliance. It was later changed into Triple Entente with Britain's entry. The was one side of the picture Alliance and counter alliance. This encourages both sides to go to war for their interests.

Another part of the story is the colonial position and arms race. Both Britain and France had colonies while Germany and Italy were new power. So Germany, as well as Italy, tried to gain a colonial position. One example of it can be found during the Second Moroccan Crisis. Russia and Britain supported French expansion which reinforce their relationships. German gunboat was deployed to Agadir (a Moroccan Atlantic port) and France deployed her troops to the interior of Morocco. Actually, Germany was not against the French expansion outside of Europe but wanted territorial compensation for herself. Germany gains territorial concessions in French Congo.

The economic growth give Germany a chance to increase her Naval Power which Britain saw as a challenge to her Navy. The  Imperial German Navy was far behind the British Royal Navy who dominated the seas and the launch of HMS Dreadnought gave her a technological edge. The early German policy was not to make Britain angry and gain as much colonial territory. However, the German high command come to a conclusion and they diverted their resource to the army and railway road infrastructure.

Italy gains some territory in the Italo-Turkish War of 1911–1912. Italo-Turkish War and the First Balkan war shrank the Ottoman Empire. The nationalism in Balkan spread for which they fought with each other most especially in the  Second Balkan War. The Great powers were able to keep these conflicts into the Balkans and did not spill to other parts of Europe.

In 1878 Austria-Hungary had occupied Bosnia and Herzegovina but it was officially annexed in 1908–1909. Balkans came to be known as the "powder keg of Europe". But the Kingdom of Serbia considered that it will be their territory one day. The Russian Empire supported the Kingdom of Serbia and encourage her to take Bosnia and Herzegovina by force if possible. The Emperor of Austria Archduke Franz Ferdinand visited the newly annexed provinces of Bosnia and Herzegovina on 28 June 1914. Members of the Young Bosnia took the opportunity and killed the Boss. This was 9/11 for the Austria imperial pride, they considered it a humiliation to be killed by a group of subjects. In other words, they saw an opportunity for Austrian expansion. Austro-Hungarian authorities encouraged anti-Serb riots in Sarajevo. Austria suspected that the Serbian officials (Black Hand) were involved in the murder of the Archduke. But the foreign ministry of Austrian-Hungarian has no evidence to prove that Serbia was involved. On July 23 Austria asked ten unacceptable demands from Serbia which was intended to provoke war. Serbia accepted all the ultimatum points except articles six and five.  Which demand the approval of Austrian-Hungarian representatives to suppress radical elements inside Serbia territory. After rejecting it  Austria declared war on Serbia. To that Russia respond declared war on Austria. It was a chain reaction. Germany declared war on Russia and France on Germany. 

Both sides mobilized some 70 million military personnel.  As a result of this, some 8.5 million soldiers perished and 13 million civilians were the victims of this war. The German high command prepared a plan for the invasion of France which was later known as the Schlieffen Plan. According to this plan, the German army will pass through Belgium as quickly as possible. Germany demands free passage from Belgium. When this was refused, German forces invaded Belgium and declared war on France on the same day. Belgium invoked the 1839 Treaty of London which make an obligation on Britain and declared war on Germany. Russia failed because of bad leadership. The war gave an opportunity to Bolsheviks to form USSR, a communist utopia.

World war I dismantled the German, Austro-Hungarian, Ottoman, and Russian Empire. After the German surrendered, they sign the treaty of  Treaty of Versailles. The terms of the treaty were harsh and were deliberately imposed because France seeks revenge for its humiliating defeat of 1871 and the territorial loss of Alsace-Lorraine. The Germans were not happy with the terms of the treaty of Versailles. They considered it as a 'dictated peace' that is imposed upon the German population. Some 132 billion gold Reichsmarks ($33 billion) Germany has to pay as war reparations. The war was started by Austria but the bill was to be paid by Germany. It was a very large sum even British economist  John Maynard Keynes criticized it and predict that it will collapse the European economy. The French high command was unhappy and think that their allies did not do enough to secure the future of France from a possible stronger Germany in the future.

This gives a sense to the ordinary citizens of Germany that they had been betrayed by those who sign the treaty. Those who supported the Weimar Republic were called ''November Criminals''. The leaders of the Weimar Republic were incapable to cope with the 1929 depression. The economic instability makes it easy for radical groups and parties like the Nazis to hold power. These circumstances make it clear for Hitler to rise to power. He promised that he would take revenge and he was destined for the destruction of Europe.