China was not a U.P.U. member in the Ching Dynasty. When the Imperial Post Office started operation in 1897, mail exchange with foreign countries had to rely on so called "Guest Posts" - alien postal organizations set up and operated in China by Western Powers. In general, each of the foreign offices handled certain area of the world.

French / Indo-Chinese Office
France, French colonies, Europe (by sea)

British / Hong Kong Office
Britain, British colonies, Europe (by sea)

Japanese Office
Japan, America

German / Kiaochow Office
Germany, German colonies, America

Russian Office
Russia, Europe (by Siberian Railroad)

U.S. Agency
U.S.

Since there had been no postal treaties between China and other countries until early twentieth century, Chinese stamps were not recognized by foreign offices. In addition to Chinese stamps franked by senders at international rate, overseas mails had to be franked with same rate of foreign stamps by Chinese office before handed to foreign offices. This double franking practice resulted so-called Combination Covers.

Combination franking was ended after the postal agreements with France (1/1/1902), Japan (7/18/1903), Hong Kong (2/1/1905), Germany (11/3/1905), and Russia (2/19/1909) went into effect. These agreements defined exchanging mail matters and recognizing postage stamps of each other. There was no postal agreement signed between China and the United States of America.