How Did The U.S. And The U.S.S.R. Get Involved In The Suez Affair?

The US and USSR became involved in the Suez Crisis of 1956, because of the Cold war which had emerged following the creation of the Communist states in eastern Europe after the Second World War.  
Ostensibly the Suez crisis was an Arab Israeli conflict.  However, both the UK and France, as well as the USA refused to help Egypt when Israel became aggressive towards her.  Nasser, the leader of Egypt then nationalised the Suez Canal Company, seizing control of it.
This annoyed both the UK and France, who then secretly colluded with Israel to wage war on Egypt.  
Egypt was then seen as friendly towards the USSR.  The USA feared that the USSR would intervene in this situation and fight on behalf of Egypt.  So  it too became involved.
The result was basically a disaster for the UK and France, with Sir Anthony Eden forced to resign as Prime Minister as a result.
However, the symbolism of this conflict is that there was a distinct change in the balance of power from Europe to a state of passive aggression between the USA and USSR.