Your statement assumes a conclusion that has not been established and indeed that conclusion is wrong in my opinion. We can tax wealth and tax money transfers out of the country and do a host of other things to equalize things. We can establish labor standards that mandate a certain level of living for workers. We can also require a high level of labor standards for imported goods.

As an extreme example of how easy it can be to better equalize the distribution of wealth, and not one that I'm advocating for, the Soviets did a great job of ensuring that economic inequality was low. Of course this was obtained by ensuring that everyone was equally poor.