Fortunately, unfortunately depending on how you view it, birthrates in 1st world nations have been on the decline for some time. Infertility is a real issue as well as increased instances of autism for births that ARE happening. Throw in the ease of access to and the socially acceptability of abortions in the West and its easy to understand some of the business and political imperative toward migrant influx from 2nd and 3rd world nations which still have a more normal birth rate.
It's a dilemma in many ways, bring in migrants to shore up a nation/society that aren't producing enough offspring to maintain needs but see that nation/society fundamentally changed by that influx of migrants that were supposed to save the day. England is very much an example of this.
Regardless of that though the point still stands that there are only so many resources that can be grown, built, mined, etc. As the world population grows so much the demands for those resources and the areas from which to gather them. One reason why war, while horrible, is probably a truly necessary safety valve for the planet and species. We have no natural predators above us on the food chain, we've progressed enough that human lifespans are probably at their greatest, medicine sees us survive more than at any other time in history, at least half the planet enjoys a level of potential nutrition our ancestors could only dream of. We've by and large tamed every environment on the planet except for the most extreme like the ocean floor and the arctic and we can at least visit those in one fashion or another.
War is unfortunately the only current means of truly culling our species and the pressures of over population and resource scarcity are going to see that to likely happen more and more often till we have a right proper world war at some point. Remember, it's mostly 3rd world nations that still seeing a boom in their population growths and those societies tend to have a more pragmatic view when it comes to taking what is needed for one's self and one's people. Their sensibilities are not those of the West by and large.