Is the environment a source of international conflict?
This depends on how you define “environment” and how you define “conflict.” There are at least two ways to define each word.
The “environment” can mean the physical world, including natural resources and territory. On the other hand, it could simply refer to environmental conservation. “Conflict” could refer to any sort of international disagreement. On the other hand, it could refer only to war. Depending on which definitions you use, the answer will be different.
For example, to my knowledge there has never been a war over the issue of environmental conservation. No country has gone to war with another because of pollution or erosion or deforestation and loss of habitat for wildlife. One the other hand, there has been plenty of conflict short of war over this issue. Perhaps the best example would be the current conflict over how to deal with issues of global warming.
There have been plenty of wars and other sorts of conflicts that have broken out over natural resources and territory. In fact, you could argue that all wars are caused by this. An example of this would be the Persian Gulf War of 1991 which started because Iraq took Kuwait, in large part because of its oil reserves.
The answer to this differs, then, depending on how you define the terms “environment” and “conflict.”