Using U.S. cross-border bank exposure data, this study establishes a line of arguments and findings, which together constitute the following observation: "Deregulation of U.S. banks, via consolidation and a volatile earnings stream, increased volatility in bank lending to emerging economies, and, in due course, worsened the financial crises in emerging economies." The volatility of U.S. bank lending to emerging economies has increased during the past twenty years. To explain the across-the-board, increasing volatility of U.S. bank emerging market claims, this study turns to the supply side of the equation: the deregulation in the U.S. banking sector that imparted this commonality to their banks' investment patterns to emerging economies. In so doing, it unveils the linkages through which U.S. banking deregulation ratcheted up the volatility of U.S. bank lending into emerging economies. It starts with the detection of a particular feature of U.S. bank emerging market lending that warrants further attention -- increasing volatility over time. Unlike bank lending from Europe or Japan, U.S. bank lending exhibited the unique feature of increasing volatility over time, regardless of its destination. By looking into domestic push factors that could have contributed to this characteristic, this study identified a temporal association between important deregulation initiatives in the U.S. banking industry and the volatility of emerging market lending by U.S. banks during the same period. This association was then explained by the linkages between the major outcomes of deregulation -- consolidation of the banking industry and diversification of banking activities -- and the increased volatility of lending into emerging economies. Together, it argues that the U.S. banking deregulation had the unintended and unanticipated side effect of increasing the volatility of U.S. bank lending into emerging economies.