Which event in 1991 was significant for the roles of the USSR and the USA?

The fall of the USSR in 1991 was a pivotal moment in global history, marking the end of the Cold War and significantly altering the balance of power between the United States and the former Soviet Union. The dissolution of the Soviet Union not only concluded decades of geopolitical tension but also led to the emergence of multiple independent republics that were previously part of the USSR. This event symbolized the victory of democratic and capitalist ideologies over communist ones, reinforcing the United States' status as the sole superpower in the post-Cold War world.

The end of the USSR also spurred a wave of political and economic reforms in numerous countries, reshaping the global landscape and prompting discussions about democracy and market economies in former communist nations. This event further allowed the United States to expand its influence internationally, both politically and economically.

In contrast, the other events mentioned, such as the destruction of the Berlin Wall and the public launch of the World Wide Web, while significant in their own right, do not encapsulate the same transformative impact on the global power dynamics as the fall of the USSR. The election of Donald Trump, occurring much later, reflects domestic shifts in American politics rather than the larger international power shifts seen with the end of the Soviet Union.