Abstract: Marx and Engels exposed the capitalist trade policy and the phenomenon of capital external expansion from a political economy perspective in their early years. In the middle of 1850s, Marx and Engels exposed the predatory nature of virtual capital speculation in countries such as Britain and France, particularly in the case of small, vulnerable nations. In the compilation of volume 2~3 of Capital, volume 3, in his later years, Engels made an important addition to capital expansion. Marx and Engels’ thought provides material and methodology for the foundation of Lenin’s Imperialism, which is of great practical significance to the understanding of the nature of western financial capital.