America's emergence as an active, operational world-power did not occur until the 1940s. During World War II and then beyond, America's industrial, military, and other capacities were finally evident as the strongest in the world. It was World War II which both marked and to a large extent caused this phenomenon.
A couple of events come to mind, part of the winning side in WW1 and WW2
World War I is significant because it marked the debut of many new types of weapons and was the first huge war to benefit from technological advances in radio, electrical power, and other technologies
Some of the results of the Spanish Armada were the Spanish economy was in trouble. The gold and the silver that Spain received from the Americas caused high inflation.It signaled the decline of great European power. It also caused Spain's economy to crash. This defeat proved that England had the power to defend itself. And in the end, England remained an independent and Protestant nation.
The first event was not in the U.S., but it is the test site of Bikini Atoll in the Pacific Ocean. Tests that were done in the 1040s and 1950s have left their mark--still radioactive after all these years. The accident at the Three Mile Island nuclear power plant near Middletown, Pa., on March 28, 1979 brought awareness of the dangers of nuclear power. Although there was no lasting environmental effect, communication to the public did raise fears.
For the allies the Americans entry was pivotal. On the Eastern Front the bloody Bolshevik Revolution headed by Vladimir Lenin had swept the Communists to power in Russia.
Supreme commander in chief of allies
The Spanish American War.
Emergence of monopoly power and concentration
The conquest of Constantinople
No single event marked Rome as the dominant power in the Mediterranean. It was more of a process than an event, one which involved victories in wars. One was the Pyrrrhic War. The First and Second Punic Wars established Rome's dominance in the western Mediterranean. The Roman-Syrian War and the Third and Fourth Macedonian Wars made Rome the great power in the eastern Mediterranean and the Third Mithridatic War ended challenges to her power and led to her dominance over Turkey and the Levant.
Both Britain and France challenged Spanish power in the Americas.
The President of India.
how did the panama canal increase americas power in the world
The Berlin Conference of 1884-85 regulated European colonization and trade in Africa during the New Imperialism period, and coincided with Germany's sudden emergence as an imperial power.
When the Tang Dynasty finally rose to power as a ruling empire.
great britains emergence as a major naval power
The conclusion of the EDSA People Power Revolution in 1986 was the ousting of President Ferdinand Marcos from power and the installation of Corazon Aquino as the new president of the Philippines. This event marked the restoration of democracy in the country and the beginning of a new era of government.