In the height of the cold war and the start of the Jewish independence war / civil war between the Arabs and the Jews in the mandate of Palestine, a resolution was passed in the UN. The partition plan of the mandate of Palestine.
At the time, Palestinian (Pre-1948 Israel) Jews were building communal settlements and they were managed similarly to the ideas of socialism. (they were basically small socialist villages)
Back to the partition plan, the soviet union voted in favour of the resolution because they saw similarities between their economic approach (socialism, communist-socialism etc.) and thought of it as a good idea to get the Jews on their side and establish a foothold in the Middle East.
Jews did not care as they saw it as an international charter, something they've been seeking after for a long time ---
(I don't know/remember what happened in between, therefore I'll skip it so you wouldn't be confused, I'll urge you to research this on your own)
As I said at the start of my reply, this was at the height of the cold war. So the US government actually wanted to vote against the resolution because they saw the Soviet Union voted in favour. However, American citizens (and american jews) were pressuring the US government to go in favour of the resolution too because of what happened to the Jews in WW2 (this was at the time when the US citizens were all for peace, love, hippy etc), So the US did.
And since then the relations between the US and Israel started to tighten. However, misunderstood by many, the US did not help Israel in any of its early wars: No help in the 1947-1949 independence war, no help in the 1967 six day war and no help in the 1973 Yom Kippur war. That's basically it.
TL;DR usa and israel tightened relations after their independence, there were however ups and downs.