What was the main motivation for the US to supply Israel with arms during 20th century?

Answer 1

The United States support for the State of Israel comes from a variety of sources. Israel has cooperated with the United States on diplomatic issues, military and intelligence exchanges, large amounts of trade, and significant technological investment. In addition, there a numerous Americans who support the State of Israel because of religious convictions on top of the already-listed reasons. As a result, the US has supported Israel with arms in order to defend such a useful ally without having to commit American boots on the ground.

Answer 2

Sadly, none of the presidents, cabinet secretaries, or members of Congress of the past 68 years
ever wrote or phoned me to explain their motivations, so the best I can do for you is to speculate.

Maybe it was because from the day of its declaration as a sovereign state, modern Israel
became the only representative democracy in the Middle East, with equal rights for all of
its citizens ... a form of government and society that we've been trying to cajole others in
the region to adopt for decades now, with very little success.

Maybe it was the fact that beginning on the day of its declaration, it was attacked militarily
by the massed armies of surrounding nations, who publicly declared that they could not
accept its existence, and who continue to publicly declare the same thing until today, and
how it might have looked to the rest of the world if the USA had allowed a close ally to
sink like a rock without lifting a finger to help them defend themselves.

Maybe it was because of the tremendous value of the technology and military intelligence
that the US gets from Israel.

Maybe it was because of the long list of US companies that have invested heavily and built
major research facilities in Israel, to profit from the vast pool of business and technical
expertise, skilled labor, and world-class educational institutions available there.

It's hard to tell for sure. It could have been any of these reasons. Maybe more than one of them.