Migration

Can migrations have a positive affect on the people/land receiving the immigrants?

I think that it can have positive affects, but it's just a matter of luck, coincidence, or sometimes actual reasons. One of the more positive sides is that there would be more worker for the land or regular work. But that will not always happen, and it may lead to overpopulation, deforestation, revolts, etc... But on the other than, if that does not happen, which it completely possible, then migration can definitely have more positive affects. for instance, the culture of the city of country will probably get much richer and develop. All those new religious, ideas and technology will spread, and be developed further. Sometimes the new ideas can lead to other, even more advances invention, or can be combined to make some very useful invention. That will usually lead to easier accomplishment of every day tasks, or maybe even new tasks, creating more jobs, and less poverty. Also, religions can mix together, or inspire other people, and maybe even make a unified religion, making the people unite, if revolts don't occur because of the unification.
Also, if the government uses the immigrants for their benefit, then they could even have a much larger army/navy. If, like the Romans took their captives into their army, that country could do the same, then they would have a stronger army, conquer more lands, and perhaps become a great empire, and long lasting.
another positive effect, is that with good circulation and development of knowledge and technology, the culture may greatly advance in their development, technology, art, and culture itself, potentially allowing a new great empire to rise.