Why America doesn't Join Any War soon, like WW2?

In the World War 1, United States of America was the part of allies force where were the other coutries like Russia, France, Belgium, Great Britain, Japan, Romania, and China. On the other hand,  Central Powers which was created by Germany, Austria-Hungary, Bulgaria, and the Ottoman Empire. 

In the time of 1917, both sides of the group have lost a vast field of amrs and troops.  The situation changed in early 1918 when Germany launched its “Spring Offensive,” intended to end the war before the Allies were reinforced by millions of Americans. At the peak of the crisis, Pershing relented and assigned American divisions to hard-pressed Allied armies. This offensive was a curse to the soldier, as we have read out this in the poem, "Spring Offensive" by WIfred Owen, that shows "Inhuman humanity". 

The United States of America had lost almost 53000 soldiers or higher than it from this war. Also they have fought less than six months. On the other hand, falling in the war, the citizen and common men of America were in wory. they always suffer in this case, the time was so lamentable to their history, as they didn't see this type of big war in human history. 

In some articles, we have found that over 60000 people were died in some accidents. As we assume like another group of the war has given amrs to the city of America, and the common people were died from this. Historians say that this is one of the deadliest wars of the human history. 

The Great Depression was started in 1929 and ended in 1939. This was one of the curses of human history which is happened in the modern age. It effects mostly in America.  The Depression was particularly long and severe in the United States and Europe; it was milder in Japan and much of Latin America.

The economic impact of the Great Depression was enormous, including both extreme human suffering and profound changes in economic policy.  

The stock market crash marked the beginning of a decade of high unemployment, poverty, low profits, deflation, plunging farm incomes, and lost opportunities for economic growth as well as for personal advancement. Altogether, there was a general loss of confidence in the economic future. Here is the reason to be Great Depression for lossing the stock market. In a time, when all the people of America of were mostly involved in the stock market, and all of them getting a lot of profits. In a speech, "After getting laugh then a cry will come to your life, as this type of event is done in America." A crash has come to the stock that's the biggest stock market crush in the stock history. After this, most of the money was in stock and people have no money for eating and living. Some of the Historians say that the rich class people have come to footpath, they all become begger. 

After all this events, America has suffered a lot of time to recover, being they are a richest country of the world. When the time comes, 1939, Hilter, from Germany has started fighting to won the world. In this case, first two years of the war America didn't join the war, untill 1941.  

Russia, France, and Britain were fighting with Germany and Japan. Here America didn't come to join in this, as she knows about her a lot losses came from World War 1 and just she has come out from the Great Depression.