What was Malthus’ theory of population growth? Do you think he was correct?
That as population increases, so does competition, and yes.
Malthus, one of the scientists that influenced Darwin and his Theory of Evolution, stated that as a population of organisms increases, so does competition. In this case, intraspecific - within the same species - competition.
In this case, they would be competing for things like food, water, mates, shelter, or anything else this particular species would need to survive.
Because all of these resources are limited, when the population grows to some point, there won't be enough resources for all. So some organisms will not get some resources, and will die.
This way, the population is kept in check by killing off all 'excess' organisms, keeping it stable.
It is also a mechanism for natural selection and so evolution, because only the weakest organisms die, and the strongest survive to reproduce and create strong offspring.
(And yes, he is correct, or at least that's what I was taught.)