Why can it be a disadvantage for a nation to depend on foreign oil?

If a nation were to depend on foreign oil, if there were be an natural event to the country the nation is depending on that would cause a problem such as decreasement of oil or make it hard to export oil it would be hard to find an alternative efficiently. If there was to be a war or feud, or you eliminate an export to the country with the oil, they might stop sending oil.

Because when a nation is dependent on foreign oil it's because they can't source any themselves so in a situation where they can't export any oil from foreign countries they are at a loss