Everyone keeps talking about government restrictions, but most countries this is not necessary. As overcrowding becomes predominant incidents of homosexuality go up- this has been documented in both rats and human populations. inherant to overpopulation is a greater opportunity for disease to flourish. Plus there are individual choices to be made- it is clearly economically advantagous to have fewer children rather than more in any developed country, it doesn't require government regulation to point this out. If water becomes scarce, food will become scarce, and the human body does not reproduce as easilly when it is malnourished.
War is only the result when we feel like we are overpopulated even though resources are abundant- a need to expand our territory. And wars are more and mre being fought between machines and poor non-industrialized countries. If we followed the ancient model of enslaving and integrating the countries we conquered it would probably be better for them in the long run than the nation building we try and do now- yes I know we don't do slavery anymore (and one could argue the problem was hereditary slavery, not slavery in and of itself, but I digress), but even if the conquered land were auctioned off as new terrirories it would help both with the debt and with the ability of those countries to develop up to our standards of living.
As to oil, yes everyone still drives or uses the bus- but if you haven't noticed gas mileage is a much bigger selling point on cars now, and more electric vehicles are being sold.