The War, although entitled "The Opium War" was in fact not about opium at all. In the race to colonize the world, China represented the last prize in the Far East for European countries. The Opium War was the first step designed to open China along with its markets and resources for exploitation.
The War itself physically opened China. However, it was the aftermath of the War that exposed China, economically, socially, politically and ideologically to the outside world. The unequal treaties signed after the Opium War were the primary mechanisms to open China.