Why is international finance necessary?

Why is international finance necessary?
Capital investment is the single most critical factor in growing an economy. Without investment, there is no growth, only subsistence.For example, a farmer can barely feed himself if he has no tools. If he has the capital to invest in a horse and plow he can feed many people. If he has the capital to invest in a tractor he can feed many more.Developing countries have a hard time getting their economies to grow because they have no capital. This is why international finance is necessary.