Explain to me Israeli support

Have read many articles over the past couple of years concerning the Israeli-Palestinian conflict and understand the basics of the conflict, I think, but I do not understand why the US Government seems to want to back Israel no matter what they do.
Examples:
1) If terrorist lives in this home then terrorist is killed and family home destroyed even if home is filled with other family members not involved.
2) Arbitrarily annex territory at whim taking over others lands Palestinians have homesteaded for years and use as Israel pleases.
3) The killing of a wheelchair bound, blind and deaf leader.

I assume there is some history to this backing and wish to know.

Dave