The Allies won ww1 mostly because they had a bigger advantage in their quantity and quality. They had also got a bigger industry for weapons and many other things. The allies were Russia, France, Britain, the United States, and some other smaller countries states. France had 777,000 French troops and 46,000 regional troops, Russia had 5,971,000 men in the Russian army, the United States had 4.7 men and women that served in the regular force, national guard units, and draft units, and 2.8 million of them were serving overseas.
In Britain, they had around 247,000 soldiers for the regular army, and over half of them were sent overseas supported by 210,000 reserves and a possible 60,000 extra reserves. This shows that, overall, Britain had the lowest number of people fighting for them and this gave the Allies a very big advantage. Ww1 lasted for four years from 28 July 1914 to 11 November 1918 and had around 15 to 22 million deaths and 23 million wounded.
By 1917(3 years of WW1) the allies, France, Britain, and Russia, were losing. Then the United States joined the war after a German U-boat sunk into the British ocean which killed 159 Americans. After America joined, Germany tried to persuade Mexico to join the war against the United States.
The Allies had loads of new soldiers so this gave Germany no other choice but to surrender. The German Army had 700,000 men in 1914, though within a week, they had 3.8 million men under arms.
They lost due to the arrival of new american troops. This was bad because the German lines were being pressured by the British, American forces, and the French. A few of Germany's allies backed down like Bulgaria and Turkey leaving Germany alone. The German war machines were tired and were lacking the ability to produce new guns and many other things and this forced them to quit.
Another very important reason was that when the U.S. entered the war and since it was a big country with a huge population and a giant industrial base, they were able to provide weapons, materials, and millions of men so the allies won just because they were able to get the US on their side.
The western front was the main place of war during ww1. The German army opened up the Western Front by invading Belgium and Luxembourg and then they gained military control in the industrial regions of France.
World War 1 began in 1914 due to the assassination of Archduke Franz Ferdinand of Austria, this murder caused war across Europe that lasted until 1918.