I heard something related to this recently. The development of synthetic rubber meant we did not need to control regions with rubber plantation. This was mentioned in association with World War II. Another interesting point discussed was that in order to send secure communication by wire you had to control the land the wire traversed to prevent disruption of the communication. The invention of wireless communication meant that you only had to control the terminals of the communication.
Assuming there is a single source, and that rival country is completely determined to stop you from getting any of it, instead of selling it to make money as normal?
More commonly they'd just put a tariff in place, which is likely cheaper to pay for than a war and occupation.
I provided context for this, WW2. The Allies were cut off from the natural rubber supply of Southeast Asia at the beginning of the war. You can read more about it here: https://en.wikipedia.org/wiki/Synthetic_rubber
