Here's my hunch: To see Shanghai today is to visualize China tomorrow.
Shanghai's epic story is a unique amalgam of East and West, a historic combination of cultures and traditions -- just like Expo. Ironically, it was through distasteful historical circumstances that Shanghai came to engage and embrace the West.
Beginning with the Opium Wars in the 1830s, foreign armies, particularly the British, attacked a self-isolated, self-weakened China, bringing the once-proud Chinese empire to its knees. The invaders forced degrading "Concessions," sections of cities sliced off and ceded to foreigners. Shanghai was carved into French, British, and American Concessions (the latter two combined into the International Concession). The Chinese became second-class citizens in their own country. It was humiliation.
However, the foreigners built schools, hospitals, electrical plants, and waterworks. There were sewage facilities and paved roads, concrete and iron bridges, trams, busses, and automobiles. Shanghai became the most modern city in China.
In the 1920's and 30's, Shanghai was the "Pearl of the Orient" or the "Paris of the Orient." Ballroom dancing in elegant hotels epitomized the era. The famous Bund, with its European-style architecture along with Huangpu River, was the center of city life for foreigners and upper-class Chinese. All the while, the poorest classes, living in shantytowns on the margins of the city, barely able to feed their children, became the mass base for the Communist revolution in the 1940's.
But with modernity came decadence and debauchery. Shanghai became a center for smuggling opium. Mafia-like gangs controlled the rackets:prostitution and gambling as well as opium. Any who crossed them suffered extreme violence.
In 1937, as part of Japan's vicious determination to conquer China, the Japanese army invaded and captured Shanghai. Although not suffering the brutal, systematic rapings and killings that people in other cities did (notably in Nanjing, not far away), Shanghai people endured terribly bitter times. After Japan was defeated, the Communists won the debilitating civil war, taking the mainland in 1949. The Chinese people "stood up" in the world and were filled with hope. But then, less than a decade later, ideological extremism visited misery on millions, first with mass political campaigns (denunciations), then mass famine ("Great Leap Forward"), and finally, China's decade-long descent into chaotic madness ("The Cultural Revolution" 1966-1976).