After conquering Korea in their 1592 invasion, The Tokugawa Shogunate went on to unify the rest of Japan and begin minor excursions into China and Manchuria. In the 1620s as the Ming Dynasty began to lose it's grip on power, the Tokugawa Dynasty came in and proclaimed itself the Emperors of China, later fully conquering Manchuria to eradicate the newly proclaimed Qing dynasty. By 1690 The Tokugawa had conquered the coast from the Amur river to north Vietnam and had begun expanding into the pacific in an attempt to compete with the Europeans who had been poking their heads in Asian affairs with increasing frequency. Once Japanese rule over China had solidified some weaker states began to pay tribute to the new Emperors of China in hopes that they would be protected from European invasion.
Within the borders of the Empire things have become relatively stable. The Shogun Rules from Shanghai due to it's strategic position on the coast of the Yellow River, and the Emperor continues to reside in Kyoto. For the sake of unity, Mahayana Buddhism is the primary religion associated with the state, however in different regions local customs and folk religions are still kept alive, most notably in Japan proper. Though attempts have been made to limit Chinese migration to Japan proper, the influence of Chinese culture continues to increase as the Empire goes on, the Japanese language gets more and more Mandarin loanwords each day, and Chinese cultural elements such as Confucianism or Chinese Gods have been becoming more and more known in the Japanese mind.
In 1740, The Spanish Empire launched an attack on the Tokugawa for their colonial expansion in the Philippines. Following what turned out to be a surprisingly long and expensive war for the Spanish they retreated from their port in Manila in 1744, signalling a Tokugawa victory. This event sent shock waves across Europe as, for the first time, a power that they hadn't known before their age of exploration had pushed the Europeans out. Was it a fluke? Are the Spanish THAT incompetent even under the Bourbons? Nobody knew for sure, but European powers began to tread lightly in east Asia.