The plague in the middle ages supposedly killed half the population. Well, the world population was much much much smaller then. On the upside, with the smaller working force afterwards, peasants demanded more rights and higher pay (well anything more than no pay would be good) In fact, most historians trace the rise of the middle class from the ravages the plague caused.
Secondly, I remember world population being 3 billion in the 1950s and people were worried then about running out of food. Intensive strides in forcing more foodstuffs to grow, plus the reduction in deaths due to the fight against disease has now resulted in world population growing to 7.7 billion -- a number that this planet really can't sustain.
I've been suspecting that another plague would hit -- and now it has.
(not that I had planned to be around when it did - but here we are.)