美國在兩岸互動過程扮演重要的角色，在美中台三角戰略關係中，「兩岸關係」及「美台關係」又受「美中關係」影響甚鉅。東亞地區不同於全球「單極體系」（unipolar system）結構，乃呈現一個「兩極體系」（bipolar system）的權力結構；美國和中國大陸兩個強權共處於此體系內，東亞的大陸區域係由中國大陸所掌控，美國則控制東亞的海上區域，構成海陸爭霸的格局。中國大陸崛起後，對於美國在東亞地區的海上霸權，以及美國在東亞地區的經濟利益帶來極大的威脅。2010年7月，美國國務卿柯林頓（Hillary R. Clinton），在參加「東協區域論壇」（ARF）外長會議時表示，美國將「重返亞洲」，為美中海陸爭霸投入重大變數。美國重返亞洲後，美中戰略關係不僅發生了變化，兩岸關係亦受到美中戰略關係變化所影響。本文嘗試釐清美中戰略關係轉變背後所隱含的複雜因果網絡，以期能對兩岸關係的發展與走向有所理解。

The U.S. factor plays an important role in the process of interactions across the Taiwan Strait. In the U.S.-China-Taiwan strategic triangle, both cross-Strait relations and U.S.-Taiwan relations are greatly influenced by Sino-U.S. relations. Unlike the unipolar system at the global level, the East Asian regional configuration of power is bipolar. The U.S. and China are the great powers in this system; China dominates the East Asian continent while the U.S. controls regional waters, resulting in an order shaped by the contention between the two powers. The rise of China has brought about major threats to both America's maritime hegemony and economic interests. In July 2010, U.S. Secretary of State Hillary Clinton's announced at the ASEAN Regional Forum (ARF) that the U.S. "is back" in Asia. Washington's policy of "pivot" or "rebalancing" toward Asia has introduced a great deal of uncertainty to the continental-maritime competition between the U.S. and China. Not only has the strategic relationship between U.S. and China changed, but cross-Strait relations have been impacted as well. This paper applies historical-structural theory to clarify the complicated web of causality behind the transformation in Sino-U.S. relations and attempts to reframe the development of cross-Strait relations within the context of Sino-U.S. relations.