Events of the 20th century have, in hindsight-propaganda, been attributed to various causes-- none of which make much real sense, or carry much factual accuracy.
It's a fact, that socialism swept over most of the world during the 20th century, and resulted in the deaths of over 1/10 the world's population through starvation, war, and outright murder. Likewise, this threatened most of the world population with nuclear annhilation-- and now results in a corporate and military industrial super-complex which has become an unstoppable juggernaut.
However, socialism only results from severe destabilization of national economic and political infrastructures, as to lead them to extremes; this is precisely what the post-Civil War US agitated in the 20th century.
Without the Civil War and resultant forcing of the states into a single pseudo-nation, the individual states became helpless to oppose both a central bank, and their forced intervention into self-serving escapades by special interests. For example, the Federal Reserve Act, the income tax, and the US intervention into WWI resulted in the Great Depression, the sacking of Germany, and the creation of the USSR; this devastation and empowerment likewise quickly led to the rise of worldwide socialism, leading to Third Reich, as well as the Rape of Nanking and the forced US entry into WWII-- basically gifting Stalin with half the globe, and nuclear weapons-- likewise resulting in the Cold War.
Without the Civil War, the states would have remained sovereign, and thus would have no indvidual interest in a common central bank; nor would they allow their citizens to be drafted to die on behalf of intervention in foreign squabbles. As a result, the Great Depression would have been circumvented entirely via simple free-market self-correction mechanisms, while WWI would have resulted in a simple standoff, and the probably decline of socialism out of its inherent inefficiency. In short, WWI would have fizzled.
In contrast, US intervention upset the balance of power in Europe, touching off a blaze which consumed the world in mass-socialism-- as well as current debacles in the Middle East from lingering fascism there, as well as land-struggles between oil-rich muslims and religious conflicts, thanks to conflicts between fanatical muslims and post-holocaust displacement and US government-created oil-addiction.
This isn't surprising, since the US had such great wealth and potential, which was turned to evil via the Civil War; it's only natural that this would lead to economic and political devastation during ensuing years. Likewise, the totalitarian control of information, which was likewise covert via the front of "free speech" (which meant speech with supported corporate statism), resulted in a self-perpetuating disaster.