As expected, the E.U. raised objections to the Oracle (ORCL) buyout of Sun (JAVA) at about the same time that the Department of Justice approved the deal. The E.U.'s objection is based on the large market share that the two tech companies would have in the MySQL software business.

European authorities have been deviling American companies for years. In 2001 they killed the GE (GE) deal to purchase Honeywell (HON), which would have been the crowning achievement of Jack Welch's tenure at the world's largest conglomerate. The E.U. has troubled Microsoft (MSFT) and Intel (INTC) over antitrust concerns, and now it has brought up similar issues with Oracle's plans.

The aggressive stance of the Europeans could threaten other deals in the works, starting with the planned joint venture in the search industry betweenYahoo! (YHOO) and Microsoft. Action on the merger could bring Google's (GOOG) huge market share in the search industry under scrutiny. Even the Kraft (KFT) deal with Cadbury might be aggressively reviewed -- if it ever happens. That transaction would give Kraft a huge portion of the gum and chocolate businesses in Europe.

M&A activity has returned slowly now that the worst of the credit crisis is over. And if the economy continues to improve, 2010 could be a tremendous year for mergers -- unless the Europeans spoil the party.

Douglas A. McIntyre is an editor at 24/7 Wall St.