Arcelor SA looks to have become its own worst enemy, as defenses constructed to fend off a hostile bid from rival Mittal Steel Co. NV emerge as the most likely obstacle to a deal between the two steelmakers.

After five months of bitter resistance, Luxembourg-based Arcelor on Sunday, June 25, capitulated to a sweetened �26.9 billion ($33.7 billion) offer from Mittal, paving the way for the steel industry’s biggest deal ever.