The United States government turned from "isolationism" to "interventionism" because of the two World Wars of the 20th century along with an ideological - and often violent - war of communism against all other ways of life., to convince most Americans to support the US government when it decided to pry into every one else's business.

Americans had generally isolationist, with a few limited exceptions, prior to being drawn into the squabbles of Europe and Asia against the will of most of its citizens.

Isolationism had become a poor option for the US in the year 1917.

In 1917, the US was pulled into a European war in order to restore peace and markets to the world. The US could have continued to stand by and watch the blood - letting for a few more years, until Europe was utterly exhausted - and largely de - populated of its young men.

After the end of World War 1, America once again swung to its natural inclination of isolationism and continued in that general orbit until the late 1930s and early 1940s, when once again world events caught up to the US of clerks, entrepreneurs, and craftsmen - an emerging economic super power - that did not wish to become an international military and political super power.

The Japanese attack on Pearl Harbour - and germany's subsequent declaration of war against the US - pulled the US into another overseas conflict. This war was even longer in scale than the war 20 years earlier, and required a much larger commitment in military deployment and in domestic military production.

The 1940s transition of the US to wartime consciousness amounted to a "new era of change" of American thinking from which the American mind has still not completely recovered.

After the unconditional surrenders of Germany and Japan, Americans were not willing to surrender the destinies of Europe and Asia to the USSR - a nation that itself would not have survived WW11 without massive US and British aide on all levels.

Most of the world economies were devastated by the end of WW11. The US was the only great power to escape largely unscathed, except for human losses and economic costs.

Militarily and economically, the US was the last man standing - the only one in a position to help Europe and Asia to rebuild markets and industries.

We shall see next what led to the Cold war between the US and the former Soviet Union and how the aftermath affected the world politics and economy.