What are some of the ways that the physical and natural environment put limits on the directions and locations of trade routes in premodern times?

Mountains or anything that blocks a pathway is hard to travel. For example in Greece there are a lot of mountains so it is hard to open trade routes on the road.

Explanation:

answer; /// i believe that one of the causes is (a loss of habitat);

question

which are human systems?

the amazon rain forest

the appalachian trail

the george washington bridge

the himalayas

the hoover dam

the north american free trade agreement