Do the mountains to north of mainland Southeast Asia hindered travel into region?

Yes, the mountains to the north of mainland Southeast Asia did hinder travel into the region.

To explain:

The mountains of the Himalayas and the Tibetan Plateau form a natural barrier between South Asia and East Asia, making travel between the two regions difficult. The mountains are high and rugged, and the passes through them are often narrow and treacherous. In addition, the climate of the mountains is cold and harsh, making travel even more difficult. As a result of these factors, travel between South Asia and East Asia was limited for centuries.