I will assume you talk about the income inequality between nations. That is, in most cases, not solvable by other countries.
To make a country (without military conflicts) better is not rocket science. You get infrastructure and education to work well in addition to limiting corruption. The corruption part is probably enough, since non-corrupt politicians will fix the rest.
After that, a generation or two later you have a South Korea. Estonia is getting there.
For examples of this, see East Europe inside the EU after 1991. The main failures with corruption are Romania and Bulgaria, which also have horrible economic inequality. The politicians even steal the money for roads!
The point is, income inequality is not a problem of economics. The problem is that packs of thieves have stolen a country/government and sucks the lifeblood out of it.