The last time multiple world powers existed alongside one another, each of them pursued a restricted trade policy with one another. Great Powers throughout history put up extensive trade barriers and criminalized trade with competing states, usually to the detriment of the rival state or its colonial holdings. As time went on and states realized that a mindset of resource extraction from its colonial holdings, to be then used to boost the local economy of their state, was actually not a good long term investment. The succeeding solution was to establish bilateral trade ties between states and nations (countries, kingdoms, etc.) instead of relying on Mercantilism.

The notion of bilateral free trade stuck, however it wasn't until the end of WWII that this began to replace the old system of trade. Where the state would purchase or extract raw materials from their colonial holdings and manufacture those materials into products which would then be added into their markets (whether those markets were local or within their sphere of influence). The reason why it was possible post-WWI and WWII is because of the fact that most of the Great Powers scaled back their ability to project both soft power and hard power. This vacuum of power was subsequently filled by the United States, which possessed the world's strongest Navy at the time, therefore giving them the authority to secure the world's trade routes by themselves without any competing powers.

The United States, unlike its European colonial counterparts, emphasized early on in their foreign policy that extractive Mercantile trade, was not the way to go. By gaining something to the detriment of a particular nation, the day will inevitably come where uprising becomes more attractive than living and will cause more civil unrest and strained relations between states (or nation, country, whatever). The United States instead of importing from their conquered territories, flooded those territories with exports, causing those countries to rely more and more on the United States for their way of life. Any disruption in that trade, caused by a Thucydides' Trap type situation where the U.S.A ceases to exist in global politics or fails to participate in it for some reason, will cause a recession, a complete overhaul of multiple countries' economies, lead to the collapse of several states and encourage geopolitical pivots with the already rising superpowers of China (assuming they don't shoot themselves in the foot again), India, Russia (potentially), the EU (potentially), Australia, New Zealand (if their claims on the continental shelf and territorial holdings go well) and even Japan. Lesser states that rely on the United States' military, power projection and the current financial and economic system will suffer the most, namely states within the Middle East, Southeast Asia and Latin America.

This is not an argument of determining whether the United States is a morally acceptable hegemon, they are in fact arguably one of the most detestable. That does not excuse the fact that their authority actually contributes to world peace despite the fact that some of their policies are morally reprehensible. As per the Hegemonic Stability Theory.

Following the advent of the Pax Americana and globalism, contrary to popular belief, we are living in the most peaceful time in human recorded history. Where a low income earner of arguably middle class possesses the privilege of being able to bathe regularly, thanks to trade, whereas the Kings and nobility of 200 years ago didn't even have shampoo or soap for regular use. Where the average mortality rate was relatively young, communication was stifled, hygiene was almost non-existent, clean and renewable energy non-existent, disease prevalent and resources that were scarce and expensive. All as a result of stifled trade between suppliers, manufacturers and retailers, all as a result when it was deemed more profitable to kill and take to the detriment of another.

War is also steadily going out of fashion where the only war for land and territory post WWII can arguably be 2014 Russia's annexation of Crimea, whose circumstances are extremely special and unusual compared to the methods that were utilized less than 100 years ago between Great Powers.

This possession of privileges within the current total population will be deprived once global trade is stifled by an emergence of various superpowers, not totally and certainly most people will still be able to bathe and eat regularly, however, any disruption in trade will have drastic consequences which can alter the way we live. Alterations which we cannot afford in our modern world.

My post is getting long, I could go into detail with the ramifications of how states are transitioning into low yield nukes and its effects on international relations or how a single, well placed proxy war can disrupt practically everyone's lives but anyway, CMV.