the only way this will change is when governments accept that until trade has a better financial ratio, people will always be on the move.
Easier said than done. If we send money there, usually it only benefits the few not the many. Should we colonize these countries again ? Should we leave them alone ?
You mentioned the environment, there are stuff we're having made in developing countries, to the detriment of jobs in our developed countries, and the environment because of how stuff is made, and the need for long distance transport (think clothing, furniture, appliances, etc.). If we start making these again in our developed countries, it's positive for the environment, positive for employment, and negative for the developing countries...
We know sending money does not work, as most former colonies have corrupt systems of governance, those systems were put in place to keep them in check, the military forces used to control empires were mostly few foreign officers and locals doing the heavy lifting, very few became republics with constitutions empowering their own people, for generations they were raised to always place others before their own, I fully agree with you that easier said than done. I am starting to think leaving them alone is best, like AA, until one accepts your situation, you cannot make the required changes.
As of now, why would a developed nation have items made in the developed world?
One is cost, due to the higher ethical standards in the developed world, you use the lower standards in the developing world to your benefit, then claim it is a local issue that workers are abused. In your clothes example, as the process of the materials became automated / mechanized, the number of jobs and their spin off effects became lower / less important than the price and profits to be made selling, as in all things, follow the money. Remember the sweat shops of kids making shoes in Asia, has that industry left?
Another is some of the technologies are potentially dangerous, better have others live under that shadow than your citizens - chemical production.
Since most developing countries are getting financing from the developed nations, it replaces "gun boat" diplomacy, the major issue facing developing nations financially is getting them to live within their means, once you don't and you pile up the debt, your future and in essence your society become fodder for those holding the loans.
The number of migrants going to Europe are they going for work, escape persecution, pushed out by their own government or looking for a better life by living on handouts?
The big key is integration, when the mass migration started to Europe, how many of those migrants are now integrated into European society, that I think will be the key for the standard of living going forward. In their own countries they had to struggle to survive, now in some instances they are taken care of, interesting realities.
No easy solutions, what we do know however, is that it is always easier to get your hands on the law abiding folks versus chasing down the illegals, the airline is licensed and regulated, easy target, ensuring that you track the pax and remove them when their time is up is much harder / difficult.