Answer:

Introduction      

The First World War (1914-1918) erupted following Archduke Ferdinand’s assassination, leading to a fierce battle between the Allied and Central Powers. Just two decades later, World War II (1939-1945) started with Germany’s invasion of Poland, pitting the Axis against the Allies. This devastating conflict ended with the atomic bombing of Hiroshima and Nagasaki and the Axis’ surrender.

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Germany’s role in both World Wars

World War I:

• Blank Cheque Assurance: After the assassination of Archduke Franz Ferdinand, Germany extended a “blank cheque” of support to Austria-Hungary. This encouraged Austria-Hungary to take a hardline approach against Serbia which escalated into a full-blown war. 
• Invasion of Belgium: Germany’s Schlieffen Plan required a quick invasion through Belgium to outflank the French armies. This invasion brought the United Kingdom into the war, in defence of the violated Belgian neutrality, drastically escalating the scale of the conflict. 
• Unrestricted Submarine Warfare: Germany resorted to unrestricted submarine warfare in the Atlantic. The Lusitania tragedy, where a German submarine sank a British ocean liner causing massive civilian casualties, was a notable incident that gradually pulled the U.S into the conflict. 
• Zimmermann Telegram (1917): British cryptographers deciphered a telegram from Germany proposing a military alliance with Mexico, in the event of the US entering the war against Germany. It stirred anti-German sentiment in the U.S, eventually contributing to the U.S joining the war.

World War II

• Violation of Treaty of Versailles: Germany, under Hitler, violated the Treaty of Versailles, which had ended World War I, by remilitarizing the Rhineland and annexing Austria. It showcased Germany’s expansionist agenda, setting the stage for another major conflict.
• Munich Agreement Betrayal: Germany violated the 1938 Munich Agreement by occupying Czechoslovakia in 1939, a blatant showcase of its expansionist ambitions, and a prelude to the broader conflict that would engulf the world.
• Molotov–Ribbentrop Pact: In 1939, Germany signed a non-aggression pact with the USSR, which had a secret protocol for the partition of Poland between them. This aggressive intent of Germany caused the beginning of World War II with the subsequent invasion of Poland.
• Invasion of Poland: Germany’s unprovoked invasion of Poland in 1939 marked the official start of World War II. This aggressive act was a clear demonstration of Germany’s central role in initiating the devastating conflict that followed.

Allied powers’ role in both World Wars

World War I:

• Entangling Alliances: Prior to WWI, the Allied powers formed a Triple Entente, comprising Russia, France, and the UK. This system of alliances turned a localized conflict into a global catastrophe as nations were dragged into war due to commitments to their allies.
• Economic and Colonial Rivalries: Allied powers, like Britain and France, had vast colonial empires notably in Africa, and the race for more territories fueled distrust and rivalry with other powers including Germany, laying a fertile ground for conflict.
• Naval Arms Race: The period saw an intense naval arms race, particularly between the UK and Germany. The building of Dreadnought-class battleships by both nations heightened tensions, creating a milieu of suspicion and competition, and contributing to the onset of WWI.
• Serbian Nationalism: The aggressive Serbian nationalism, notably the Black Hand terrorist organization, played a pivotal role in igniting the initial spark for the war through the assassination of Archduke Franz Ferdinand of Austria-Hungary, a central power.

World War II

• Appeasement Policy: The Allied powers, especially Britain and France, tried to appease Germany, allowing it to violate the Treaty of Versailles and annex territories, with the hope of avoiding another war. This policy failed as it gave Germany time to become a formidable military power. 
• Economic Sanctions: The imposition of economic sanctions on Italy, after its invasion of Ethiopia, exacerbated tensions. These sanctions angered Italy and pushed it closer to Germany, strengthening the Axis powers.
• Failure to Support Spanish Republic: The lack of support from the Allies to the Spanish Republic during the Spanish Civil War facilitated the rise of a fascist government under Franco, who later supported the Axis powers during WWII, thus indirectly strengthening the Axis forces.
• Delayed Opening of Second Front: The Allies were slow in opening a second front in Europe, which allowed Germany to consolidate its hold over Eastern Europe. It led to a significant loss of life and gave Germany a strategic advantage for a considerable period during WWII.
• Harsh terms of the Treaty of Versailles: It imposed debilitating reparations and territorial losses on Germany post-WWI. The stringent terms fostered deep resentment, which facilitated the rise of extremist groups, like the Nazis in Germany, eventually catalyzing the outbreak of WWII.

Conclusion

Thus while Germany and the Axis powers had a substantial role in initiating and escalating both World Wars. A holistic perspective reveals that the responsibility is shared, and it does not entirely absolve the Allied powers from their role in the initiation and escalation of the wars. It is a testimony to the intricate web of international relations where actions of one entity reverberate, escalating conflicts to unforeseen proportions.