Hinduism and Buddhism are both part of the major religions in the world today. They are also some of the oldest religions that have existed continuously. Both religions have their roots in India from which they have started to spread around.
By 500 CE, the Hinduism managed to spread in the regions of South Asia and Southeast Asia, with the spreading in Southeast Asia being mostly through trade with the region. The people in this region found it very appealing so they started to accept it as their religion.
The Buddhism managed to spread in South Asia, Southeast Asia, and East Asia, with the spreading in Southeast and East Asia being through trade, just as it has been the case with the Hinduism.
Over time though, the Buddhism lost its dominance in South Asia, but it became dominant in the continental part of Southeast Asia and in East Asia, while the Hinduism lost its influence in Southeast Asia, but became the dominant religion in South Asia.