NEW YORK ( The Deal) -- Banks have been forced to re-think their approach to M&A as a wave of global regulation alters the appeal of deals and divestments. After three decades of consolidation -- epitomized by Bank of America Corp.'s acquisitive growth to transform itself into a national coast-to-coast universal bank -- a trifecta of economic weakness, regulatory uncertainty and shareholder aversion has produced a stagnant market for bank M&A.Now, five years after the collapse of Lehman Brothers, new strictures are causing banks to think twice about whether the benefits of a transaction outweigh the cost, complexity and regulatory burdens of greater size or diversification. C), JPMorgan Chase ( JPM), Bank of America ( BAC), Goldman, Sachs ( GS), Morgan Stanley ( MS), Wells Fargo & Co. ( WFC) and State Street ( STT). Sandler O'Neill + Partners investment banking group principal Tom Killian points to so-called speed bumps or asset thresholds, which may cause banks to re-evaluate the merits of a deal if it brings additional regulatory and capital burdens. But he still expects active pockets of M&A between these hurdles, suggesting the $15 billion to $50 billion asset range will be an busy area for bank M&A. The "speed bumps" occur at $500 million in assets, when banks become subject to Basel III capital ratios; $10 billion, when they must undergo Federal Deposit Insurance Corp. risk assessment and stress tests; $15 billion, when they lose the ability to grandfather trust preferred securities as Tier 1 Capital; $50 billion, when they become subject to detailed stress testing, financial reporting and potentially the Basel III liquidity coverage ratio; $250 billion, when banks are subject to the January 2014 adoption of Basel rules and stricter regulation (under Advanced Approaches rules); and lastly, when banks are deemed global SIFIs and must abide by a supplementary leverage ratio and the global SIFI capital buffer. DLA Piper partner Michael Reed says banks are likely to be particularly cautious about deals that push them across the $10 billion asset threshold. But Lazard's Spencer says regulation alone is unlikely to kill deals that are otherwise based on sound fundamentals. "If it brings them over $10 billion in assets and it makes sense, they should still do it," he says.