Read first : What caused the outbreak of World War I(1914-1918)?
The war planning and execution were heavily influenced by the invention of weapons like machine guns, rapid firing artillery guns. Almost all the battling nations possessed and aware of the new weapons.
The military, industrial and demographic resources of Allied powers (Great Britain, France, Russia) was greater than the Central powers (Austria-Hungary, Germany).
Great Britain vs Germany:
British army was considerably smaller than the French or German armies at the start of the war but it was the only army made up exclusively of volunteers.
At the beginning of the war there were nearly 247,000 British soldiers and British Indian Army was called for assistance which comprised nearly 80,000 soldiers.
The cavalry(soldiers who fought on horseback) division was armored with heavy artillery like rifles, machine guns, pounder guns than any other counterparts army.
The Great Britain's industrial development that produced steel for war weapons was higher than the German's Industrial strength.
British also showed more superiority in sea power than the German navy holding most number of dreadnought ships, battle cruisers, destroyers, submarines having extremely large guns.
Germany vs Russia:
German army owned soldiers with high state of discipline, training, leadership than any other army. German senior officers proved to be more skilled in directing a war and perform attack operations using defensive tactics.
Germany fielded more than 5 million men which made German army the second largest where Russia being the first with 15 million soldiers. Since Russian army had low scale of weapons, poor leadership and training there was an approximate balance of forces that prevent either side from gaining quick victory.
Germany and Austria had an advantage of "interior lines of communication" which enabled them to send their troops to any critical point via short route.
Germany possessed one of the fastest railway network which can transport the troops from west to east in 4 days.
Germany had a strong chemical industry and German chemist Fritz Haber was strong in developing explosives.
Nearly one million French soldiers were ready for war. Each year men turning 21 would be inducted into the French army and spend 3 years in active service training.
The French army is known for organized and strategical attacks.
Austro-Hungarian army had a vast man-power of about 3.5 million soldiers. They also had quite number of reserve troops to replace the losses regularly.
However Austro-Hungarian soldiers were of poor quality. About one-quarter of them were illiterate and they did not speak or understand German or Hungarian.
Serbian army had nearly 450,000 soldiers but did not have much soldiers for replacement like Austro-Hungarian army.
The shortage of man-power forced Serbian army to recruit under and over aged soldiers.
Among all the nations Serbia had a poor financial status and hence it lacked much of the modern weaponry and equipment.
They had no proper uniforms and were wearing civilian clothes with military coats. Serbian troops did not have service issued boots as well and majority wore footwear made of pig skin.