what were the three mistakes that president wilson made trying to get senate approval for the league of nation

Answer 1

I don't know if these are "THE" three, but they are important ones (and at least the first two are likely on the list):

1) Refused to accept ANY of the Senate's "reservations"/modifications... with which it most certainly would have passed

2) choice of negotiating team - esp. failed to involve ANY Republican Senators in the treaty negotiations (even though they were the majority in the Senate, whose support he needed for ratification)

Henry Cabot Lodge (GOP Senate leader at the time) said as much
http://156.33.195.33/reference/reference_item/Versailles.htm

3) 'burnt himself out' with his travels around the country to drum up support, so was weakened, less able to engage in constructive discussions with the Senate (This activity, against expert advice, may well have contributed to his dibiliating stroke... it is possible, however, that underlying health issues help explain his stubbornness at this time.)

Answer 2

First he went against the right during the war and followed the advice of his college grads who where now missionaries in Armenian who thought they could stop the Genocide he even would follow the advice of his diplomats on this.
After the war he felt guilt over the 1.5 million people who died starved rapped, and enslaved. The first genocide of the 20th century.
The right were so made they fought him tooth and nail from one Congressman and his health started to fail.
Unable to continue and with England and Frances self serving imperialistic goals he could not keep up the fight and than the middle east was split up. England wanting free trade through Turkey from Iran and France with its needs of trade from North Africa. And today with out the considerations of Tribe, religion , and Sects of these and many other factors the fall of the Ottoman empire which was this entire area and sided with Germany fell apart and no one was left to see that the articles of Versailles treaty were kept.

Answer 3

His biggest mistake was conjuring up the notion of a league of nations. One of the biggest failures of all time.