Sino-US relationship is one of the most important bilateral relationships in the world. Among the various factors that influence Sino-US relations, the Taiwan issue is of particular importance. The international pattern during the Civil War period and the external environment facing the US over the unification issue at that time were similar to the current international pattern and the external environment facing China over its Taiwan issue. In the international pattern before the Civil War, the European countries were the chief protagonists. Calculated by comprehensive national strength, the UK ranked the first, followed subsequently by France, Russia, Prussia, Australia and the US. Other sub-powerful nations were Spain, Holland and Italy. Economically and militarily, the US was incomparable with the UK, France and Russia. At that time the UK and the US were in a hostile state. The Southern states of the US conspired to separate from the Federal. The UK was their biggest supporter. Nevertheless, the interference of the UK with other European powers failed to prevent American unification. Therefore, research on the international relations during the Civil War period can benefit us in coping with current Sino-US relations and accomplishing the great course of the unification of our motherland.