Answer:
Wing and definitions:
At the center of all the tensions that preceded World War I was the dispute between Germany and France over territory, particularly the Alsace-Lorraine region.
Another notable dispute was between Austria-Hungary and Serbia, with claims to Bosnia. Austria-Hungary also had conflicts with Russia and other Balkan countries desiring to rule over the Balkans.
Most of the countries of Europe had prepared for war for decades, building up huge stockpiles of weapons for land, air, and sea combat, which had become more deadly and more powerful.
They required all males who reached the legal age, usually about 19, through conscription, also known as the draft, to serve for two to three years in the active military, and then for several years in reserve.
Despite attempts to reach a peaceful settlement after the assassination of Archduke Ferdinand, Austria-Hungary declared war on Serbia, July 28, 1914, triggering the chain reaction of the alliances. Russia then declared war on Austria-Hungary in response to an alliance with Serbia, Germany then declared war on Russia, France declared war on Germany, but did not actually declare war on Germany until Germany declared war on, and then attacked, neutral Belgium. Although both sides mobilized their troops and launched their planned attacks, neither was successful in achieving their objectives in the first year of war, which resulted in four years of trench warfare in which both sides suffered high casualties. Rapid fire weapons, such as machine guns, were the deadliest weapons of the war. With combat stalled on land for over 22 months, Germany attempted to draw the British into a major battle in the North Sea, known as the Battle of Jutland, but failed to destroy the British Royal Navy.
Germany relied on merchant ships for many products of war, but especially food, so the British use of the Royal Navy to block German ports to interrupt that trade was devastating. Lacking the number of ships of the Royal Navy, the Germans resorted to using submarines to enforce a blockade around Britain. This was successfully harming Britain, so British started using convoys to ambush Germans at sea. Aircraft had very little role in the war beyond scouting for the armies. Once they were armed with machine guns and bombs, they became powerful weapons.