1. Military Action Officially Begins…
Once Russia mobilized, Germany moved fast…enacting the “Schlieffen Plan”
Germany stuck in a tough position between France and Russia, so it has to move fast
The Schlieffen Plan
The Schlieffen Plan was created by General Count Alfred von Schlieffen in December The Schlieffen Plan was the operational plan for a designated attack on France once Russia, in response to international tension, had started to mobilise her forces near the German border. The execution of the Schlieffen Plan led to Britain declaring war on Germany on August 4th, 1914. 
In 1905, Schlieffen was chief of the German General Staff. Europe had effectively divided into two camps by this year - Germany, Austria and Italy (the Triple Alliance) on one side and Britain, France and Russia (the Triple Entente) on the other. 
Schlieffen believed that the most decisive area for any future war in Europe would be in the western sector. Here, Schlieffen identified France as Germany's most dangerous opponent. Russia was not as advanced as France in many areas and Schlieffen believed that Russia would take six weeks to mobilise her forces and that any possible fighting on the Russian-German border could be coped with by the Germans for a few weeks while the bulk of her forces concentrated on defeating France.
Schlieffen concluded that a massive and successful surprise attack against France would be enough to put off Britain becoming involved in a continental war. This would allow Germany time (the six weeks that Schlieffen had built into his plan) to transfer soldiers who had been fighting in the successful French campaign to Russia to take on the Russians. 
Schlieffen also planned for the attack on France to go through Belgium and Luxemburg. Belgium had had her neutrality guaranteed by Britain in so his strategy for success depended on Britain not supporting Belgium.
The Schlieffen Plan was revised as tension in Europe increased. However, the basic mechanics of it remained the same: 
a devastating attack on France via Belgium as soon as Russia had announced her intention to mobilise.
a holding operation on the Russian/German border to be carried out if necessary and if required.
Germany had 6 weeks to defeat France.
Germany would then use her modernised rail system to move troops from the French operation to the Russian front.
Russia would then be attacked and defeated.
The Schlieffen Plan was daring but it had a number of glaring weaknesses:
The actions of Russia determined when Germany would have to start her attack on France even if she was ready or not.
It assumed that Russia would need six weeks to mobilise.
It assumed that Germany would defeat France in less than six weeks.
In fact, the attack in August 1914 nearly succeeded and was only defeated by the first Battle of the Marne. Poor communication between the frontline commanders and the army's headquarters in Berlin did not help Moltke's control of the campaign. Also the withdrawal of German troops in response to a higher than expected threat on the Russian front, meant that the Germans did not have the military clout that Schlieffen had built into his original plan. It was a plan that nearly succeeded but its success could only be measured by being 100% successful. France had to be defeated - and this did not happen. Schlieffen's speedy attack and expected defeat of France never occurred - it's failure did usher in the era of trench warfare that is so much linked to World War One.

2. This plan meant an immediate attack on France, to knock them out of the war
Then Germany could concentrate on Russia

3. To reach France as fast as possible, Germany invaded the country of Belgium…
big mistake

4. The invasion of a neutral country enacted another alliance…bringing Great Britain in to protect Belgium

5. The Main Sides are Drawn
Within one week, all major powers of Europe have been drawn into the war, and taken their sides:

6. CENTRAL POWERS: Germany Austria-Hungary Ottoman Empire
Germany - Germany had the largest army and was the primary leader of the Central Powers. Germany's military strategy at the start of the war was called the Schlieffen Plan. This plan called for the quick takeover of France and Western Europe. Then Germany could concentrate its efforts on Eastern Europe and Russia.
Austria-Hungary - World War I essentially began when Archduke Ferdinand was assassinated. Austria-Hungary blamed the assassination on Serbia and subsequently invaded Serbia setting off a chain of events that resulted in the war.
Ottoman Empire - The Ottoman Empire had strong economic ties to Germany and signed a military alliance with Germany in The entrance into the war led to the eventual downfall of the Ottoman Empire and the formation of the country of Turkey in 1923.
Bulgaria - Bulgaria was the last major country to join the war on the side of the Central Powers in Bulgaria claimed land held by Serbia and was eager to invade Serbia as part of the war.
Germany: Kaiser Wilhelm II - Wilhelm II was the last Kaiser (emperor) of the German Empire. He was related to both the King of England (George V was his first cousin) and the Tsar of Russia (Nicholas II was his second cousin). His policies were largely the cause of World War I. He eventually lost the support of the army and held little power by the end of the war. He abdicated the throne in 1918 and fled the country.
Austria-Hungary: Emperor Franz Josef - Franz Joseph ruled the Austrian Empire for 68 years. When the heir to his throne, Archduke Ferdinand, was assassinated by a Serbian nationalist, he declared war on Serbia beginning World War I. Franz Joseph died during the war in 1916 and was succeeded by Charles I.
Ottoman Empire: Mehmed V - Mehmed V was Sultan of the Ottoman Empire during World War I. He declared war on the Allies in He died just before the end of the war in 1918.
Bulgaria: Ferdinand I - Ferdinand I was Tsar of Bulgaria during World War I. He gave up his throne at the end of the war to his son Boris III.
The Central Powers were also known as the Quadruple Alliance.
The name "Central Powers" comes from the location of the main countries in the alliance. They were centrally located in Europe between Russia to the east and France and Britain to the west.
The Central Powers mobilized around 25 million soldiers. Around 3.1 million were killed in action and another 8.4 million were wounded.
Each member of the Central Powers signed a different treaty with the Allies at the end of the war. The last, and most famous, treaty was the Treaty of Versailles signed by Germany.

7. ALLIED POWERS: Russia France Serbia Great Britain
France - Germany declared war on France on August 3, France had been preparing for war after Germany and Russia went to war. The majority of the fighting along the Western Front took place inside of France.
Britain - Britain entered the war when Germany invaded Belgium. They declared war on Germany on August 4, British troops joined French troops on the Western Front to stop the advance of Germany across Western Europe.
Russia - The Russian Empire was an early entry into the war. Germany declared war on Russia on July 31, They expected that Russia would defend Serbia against the invasion of Serbia by Germany's ally Austria-Hungary. The Russian Empire also included Poland and Finland. After the Russian Revolution, Russia left the Allied Powers and signed a peace treaty with Germany on March 3, 1918.
United States - The United States tried to remain neutral during the war. However, it entered the war on the side of the Allied Powers on April 6, 1917 when it declared war on Germany. Around 4,355,000 American troops were mobilized during the war with around 116,000 losing their lives.
Other Allied countries included Japan, Italy, Belgium, Brazil, Greece, Montenegro, Romania, and Serbia. France: Georges Clemenceau - Clemenceau was Prime Minister of France from 1917 to His leadership helped hold France together during the most difficult times of the war. His nickname was "The Tiger." Clemenceau represented the French at the peace talks and advocated for harsh punishment for Germany.
Britain: David Lloyd George - Lloyd George was the Prime Minister of Britain during much of the war. He was an advocate of Britain entering the war and kept the country together during the war.
Britain: King George V - King of Britain during the war, George V was a figurehead with little power, but often visited the front to inspire the British troops.
Russia: Tsar Nicolas II - Tsar Nicholas II was leader of Russia at the start of World War I. He entered the war in defense of Serbia. However, the war effort was disastrous in the eyes of the Russian people. The Russian Revolution occurred in 1917 and Nicolas II was removed from power. He was executed in 1918.
United States: President Woodrow Wilson - President Woodrow Wilson was re-elected on the platform that he kept America out of the war. However, he was given little choice and declared war on Germany in After the war, Wilson advocated less harsh terms on Germany, knowing that a healthy German economy would be important for all of Europe
Belgium declared itself as neutral at the start of the war, but joined the Allies after they were invaded by Germany.
It is estimated that around 42 million military personnel were mobilized by the Allies during the war. Around 5,541,000 were killed in action and another 12,925,000 were wounded.
The two Allied countries with the most soldiers killed were Russia with 1,800,000 and France with around 1,400,000.
Vladimir Lenin became the leader of Soviet Russia after Tsar Nicholas II was overthrown during the Russian Revolution. Lenin wanted Russia out of the war, so he made peace with Germany.
The United States was never an official member of the Allies, but called itself an "Associated Power."