How did crusades help open trade routes between europe and the middle east?

The effect that Crusades had on trade was that it opened up new trading markets, new ideas to Europeans; Europeans began to sell their own spices by trading with middle East without middlemen, this strengthening its economy.

Explanation:

nothing certain is known about what happened, but it seems that the country declined gradually, perhaps due to bad government, or, more likely, due to a series of bad harvests, which resulted in widespread and recurrent famine.

geography

this is because warmer climates often don't get people sick from the flu and regions where it was often colder more people received the flu. hope this if you need more reasoning i am here to