The World 2050

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The US won't exist, it will disintegrated into separate political entities.

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Towards the latter half of this century, there will be another huge immigration wave (this time coming from the Islamic world and sub-Saharan Africa) into the United States rivaling that of earlier waves.  It will be substantial enough that Islam will become the third largest religion in America, surpassed only by Catholicism and Protestantism.  

I could definitely imagine a huge wave of immigration coming in the next few decades, to make up for the declining birthrates in the developed world.  But I see no reason why the bulk of the immigration to the US would come from the Islamic world.  Presumably, it would still largely come from Mexico.

I don't see how the Mexican migration could be maintained it would have to slowly come down as the population of the home country decreased and the population was spread out more.

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If there is a "cure for everything", then presumably medical costs would decrease due to early prevention and quick healing.

No, because the "cure for everything" in good against viruses, cancers, germs, etc... but not against the natural problems associated with aging, which will have more effective, but more costly treatments by the time frame we are discussing.  The ability to mass clone white blood cells, also (for instance) will not prevent you from having heart problems, or from needing a knew Kidney.  We will have the ability to treat these problems more effectively, but more expensively as well.

I also imagine, BTW, that there will be a movement of people who will seek a life rejecting all these more extreme, unnatural life expanding measures.  They'll make up a decent sized subset of the population... 20 percent, perhaps.  One might suppose that this group would be made up of an "alliance" of naturalists and religious types, but I suspect that they will be one in the same at this point, as conservative religious types will slowly turn more towards naturalistic views of the Earth, in contrast to the increasingly fast pace of technological advancement.

I doubt cancer could ever be cured, I hope I'm wrong but I think it's something nature intended to exist to control our populations.