i will try to explain very brief with 2 better pictures.
First one is our Earth . If some people want a bigger slice of pizza, some other are required to get a smaller one .
If we want a want a bigger slice , we either increase the pizza size , or we need to take a bigger slice from our neighbour .
Increasing the pizza size would have resolved the problem without conflicts , but look at the second picture , the world population during ages:
We were able indeed to increase the pizza size over the ages , but the population always grow too , the competition for everything being there . And, looking at the graphic, we see an exponential growth , not a normal one . It was obvious that some population always got in competition with others for land , resources,oil, metals, minerals , forests ...
The bad new is we are not be able to keep increasing the pizza size , cause we live on a finite piece of rock .Earth. There is a limit somewhere.
But looking at the graphic , the situation in the future is not looking more promising then the one in the past . More people will be in competition for same / or less resources , and this always transform in wars . The history proved it.
The reasons for wars ? The leaders always invent one . The masses need a "casus belli " to raise at war . And as we saw, they are very good at brainwashing them . And thrown them against each other . They can always appeal to religion , race , history ...