From my understanding, America started taking a more proactive stance in global geopolitics towards the end of nineteenth century. After World War 1, America was strongly involved in the economic rehabilitation of Europe before it entered a period of isolationism in the 1930s. I've read and heard references to "American hegemony" during the 20th century, so around when exactly did America establish itself as a hegemon, and was there a pivotal event that marked America's arrival as the greatest of the world powers?
The second part of my question has to do with the Cold War. If America was indeed a hegemonic power why was the USSR able to challenge America in geopolitics so strongly during the Cold War? I've read that American industrial and militaristic capabilities were unmatched during the second half of the nineteenth century. If America was truly so powerful, why did the Cold War wage on for as long as it did?
I understand this is a super loaded question, I'm trying to contextualize and understanding America's strength in the 1900s. Thanks so much :)
While there are many metrics one can use to assess the relative strengths of any nation in regards to geo-political impact, the answer to your question is, in one respect, simple.
Hegemonic domination, if one could claim it so, began for the United States with the Bretton Woods agreement of 1944.
The reasons for this were mostly economic but had staggering geo-political ramifications. Bretton Woods establishes three core foundations for US power that had not been present beforehand.
The first was it’s unprecedented agreement that all shipping by the signatories would be protected by the US Navy. This would break the cycle of each trading nation needing to build up military naval assets in order to protect their merchant ships, granting the first true global protection for shipping.
Of course it was expected that those nations who could, would join with America in aiding in the protection of shipping, thus laying the foundation for the largest military alliance of the modern era, the North Atlantic Treaty Organisation.
Secondly, by removing any and all floating currencies, Bretton Woods required that at least one nation become the fixed point in the global financial markets. That nation was the United States. By fixing US Currency to the price of gold (around $35 per ounce), and then fixing other currencies to the dollar, not only did this prevent the disruption of fluctuating currencies, it also made the US$ the global reserve currency.
Crucially if any nation wished to purchase gold (given that it is estimated that by 1944 up to 75% of the worlds gold reserve was in US possession) they would buy it in dollars.
It was this that gave the United States the economic position that has previously been held by London. Indeed the British recognised that ratification of Bretton Woods would signal the end of their position as global leader financially, which led to a brief delay in ratification by Westminster (finally dropped after the UK realised it needed a rather large loan from the United States).
Finally, while Bretton Woods was principally and in all ways an economic agreement (and a highly successful one at that), the crucial element was that in order for it to work, all signatories had to align in terms of diplomatic and foreign policy. The US removing tariffs on all goods sold from signatories was a powerful incentive, but while not explicate, the implicate understanding that the US would have a degree of say over your nations foreign policy was there from the get-go (and is one of the reasons the Soviets, while agreeing to many of the principles of Bretton Woods never signed up to it; the other reasons being mostly ideological).
It was Bretton Woods that laid the foundation for the global influence America began to have in the late 40’s and early 50’s; crucially it facilitates American economic and thus political influence expand to match its military might.
The Soviet Union was able to match the United States due to it simply refusing to partake in Bretton Woods and offering a viable (if economically unsustainable) alternative (aka nations could avoid the need for Bretton Woods due to heavy subsidies from the Soviet Union). And while the Soviet Union presenter a military threat to the United States it was unable to match it economically, a factor that became apparent after 40 years or so.