The 20th century is a turning point in human history, where seismic geopolitical shifts from tranquility to turmoil dominated the globe. A deeper understanding of these complexities and the political landscape enables one to gain salient insights into the world today. The century brought with it profound changes that still reverberate powerfully in our current age.

Beginning in the early 1900s, the world witnessed the crumble of empires, the rise of nations, the recoil of supranational unions and the initiation of globalization – all through the lenses of two World Wars and a prolonged Cold War. Communism and Democracy, socialism, and capitalism, these became the critical poles around which global alliances and conflicts were tethered.

World War I, which rose out of the convoluted net of European politics, reshaped the political landscape as no other event had before. The demise of old empires like the Ottoman, Russian, German, and Austro-Hungarian, gave birth to a multitude of new, smaller nations. The Treaty of Versailles, which was intended to enforce peace, fertilized the roots of another global conflict two decades later by creating a sense of vengeance among Germans.

The cataclysmic event of World War II, in turn, was a manifestation of the rise of fascism in Germany and Italy, along with militarism in Japan. The world saw destructive power of a new magnitude. The Holocaust caused genocide, and atomic bombs introduced the potential to annihilate humanity as never before. This event foregrounded the emergence of the United States and Soviet Union as superpowers.

The Cold War, the half-century dread that followed, saw a steady polarization as countries aligned with either the US-led capitalist West or the Soviet-led communist East. The geopolitical rivalry between the two superpowers was largely played out in developing nations, in the form of proxy wars, ideological warfare, and economic struggles.

This era saw the decolonization of Africa and Asia and the birth of many new nations. The creation of the United Nations and other international institutions represented the transition towards a more collective approach addressing global concerns. The non-alignment movement became prominent, and independent economic ideologies evolved in regions like Latin America and the Middle East.

The collapse of the Soviet Union towards the end of the century marked the end of the bipolar world structure, leaving the US as the sole superpower. Liberalism was celebrated while former communist countries scrambled to find their place in the new world order.

The architecture of the political spectrum in the 20th century also hurled the world into a new phase: globalization. The ease of movement of capital, goods, and people became increasingly significant, as did information technology and the rise of the internet.

However, the residue of imperial history was not done with the world. Nationalism continued to play an essential role in shaping world politics, leading to the fragmentation of nations and conflicts in various parts of the world.

In conclusion, the 20th-century political landscape is a convoluted web of ideologies, alliances, and events which created a series of cause and effect scenarios that shaped the history of the globe. They not only enriched the chapters of the past but also created the foundation and trajectory for the future.