In 1914, Germany used the Schlieffen Plan to invade France, aiming to avoid a two-front war. Initially successful, it faced challenges like Belgian resistance and logistical issues. The First Battle of the Marne marked the failure and trench warfare.

The Second Battle of Ypres in 1915 marked the first large-scale German poison gas attack, causing panic and devastating losses, highlighting the brutality of the war and the adoption of gas masks.

The Battle of the Somme in 1916 resulted in significant casualties and the first use of tanks by the British. Despite modest gains, the war continued, with the Battle of Cambrai demonstrating the potential of tanks and foreshadowing the future of mobile warfare.

In 1917, Russia faced a deep internal crisis due to war, economic strain, and discontent. The Provisional Government launched the Kerensky Offensive, but it failed due to demoralized soldiers and counterattacks.

The Russian Revolution in 1917 led to the Bolsheviks gaining power in Petrograd, aiming to end Russia's involvement in the war, and by December 1917, negotiations began for an armistice.

After the Russian Revolution, peace negotiations between the Bolshevik government and Central Powers stalled, leading to Germany's Operation Faustschlag in February 1918. The Germans advanced into Russia, leading to the Treaty of Brest-Litovsk.

The Battle of Jassin in 1915 marked the beginning of the East African Campaign, where German forces defeated a British garrison, boosting morale and defining the campaign.

The Allies attempted to defeat von Lettow-Vorbeck's forces in the war, with the Battle of Tabora in 1916 securing a victory. Despite defeat, von Lettow-Vorbeck continued his guerrilla campaign, crossing into Portuguese East Africa and capturing supplies.

In 1917, von Lettow-Vorbeck's East African Campaign continued, despite facing encirclement and capturing valuable supplies at the Battle of Ngomano, showcasing his guerrilla warfare skills.

Japan seized Tsingtao in 1914, establishing itself as a rising power in East Asia, leveraging Germany's European preoccupation and gaining Britain's allyship, marking the beginning of Japan's involvement in WWI.

The war in East Asia exposed internal tensions within the British Empire's colonies, such as the Singapore Mutiny in 1915. The revolt exposed British control over colonial troops and the global implications of the conflict.

Japan's East Asia ambitions included military conquest and diplomatic expansion. In 1915, Japan presented China with the Twenty-One Demands, aiming to expand control over China's territory and resources. China accepted the demands, sparking tension and alienating other powers.

The war ended Ottoman rule in Arab lands, with Damascus' fall in 1918. Arab Revolt leaders celebrated independence, but colonial mandates crushed Arab unity.

The Sykes-Picot Agreement of 1916, a secret pact between Britain and France, divided the Ottoman Empire's Arab lands, causing anger and paving the way for the modern Middle East.

The Gallipoli Campaign, fought between 1915 and 1916, was a crucial battle for the British Empire, involving the Allied Powers, but ultimately failed due to Ottoman resistance, defining Turkish nationalism.

Germany's aggressive submarine warfare strategy in 1917, involving military, civilian, and merchant ships, led to the US entering the war. The Zimmermann Telegram, intercepted by British intelligence, convinced President Wilson and Congress to defend American interests.

The Battle of Coronel in 1914 marked Britain's first naval defeat in over a century, highlighting the global nature of naval warfare in World War I, with engagements occurring in the Atlantic and oceans.

The sinking of the RMS Lusitania in 1915, resulting in 1,198 deaths, was a pivotal event in World War I, sparked public outrage and heightened tensions between the US and Germany.