In the late 14th century Tamerlane sent at least five victorious expeditions to Moghulistan, seriously weakening Qamar ud-din's regime. The Moghuls had sent an unsuccessful supplication to the Hongwu Emperor of China pleading for help, as Tamerlane had also wanted to conquer China. Although a military alliance did not result, the Ming dynasty opened up caravan trade to Moghulistan, greatly enriching the Moghul rulers who collected zakat (tax) on the lucrative Silk Road trade. This trade ushered in an era of economic and cultural exchange with China, in exchange for the state accepting (what the Ming saw as) tributary status to the Ming.