Dealmaking in the United States has made its strongest start to a year since Reuters records began in 1980, climbing 52 percent year on year to $746.9 billion in the Jan. 1 to May 28 period. Merger and acquisition activity was boosted this week when Charter Communications said it would acquire larger rival Time Warner Cable for $56 billion and Avago Technologies agreed to buy rival chipmaker Broadcom Corp for $37 billion.