| The dismal science|
Autarky is economic self-sufficiency. A national economy which can independently exist is an autarkic economy. Autarkic economies don’t rely on international trade.
No national economy in the contemporary world is fully autarkic. North Korea is probably the closest, with its state ideology Juche (roughly translated as "self-reliance") containing a heavy dose of it. However, while the final goal is full autarky, it is still not a true autarkic economy, since it trades with China and relies heavily on grain imports and international aid to prevent its population from starving to death.
Autarky has some military benefits. Most of the world's major powers during World War II relied on it, with it being most pronounced with the Axis powers (German and Japanese imperialism were motivated in large part by resource concerns) but with the US and Britain also implementing autarkic wartime measures. The communist world, particularly under the Stalinist model of "socialism in one country", also leaned heavily on autarky, with the Eastern bloc existing effectively separate from the rest of the world outside the black market. Apartheid South Africa, during its late-period global pariah status, was effectively pushed into autarky as boycotts, divestment, and sanctions effectively isolated it from global trade. Spain was for some years after World War II also almost entirely isolated from the rest of the world due to Francisco Franco's fascist dictatorship. As autarky is a (somewhat) sensible policy if the whole world actually is out to get you and tries to subjugate you through embargoes, it has often been attempted by deranged leaders suffering from some form of paranoia. Albanian dictator Enver Hoxha, who came to believe that NATO, the Soviet Union, and ultimately even China[note 1] were out to get him, thought that only autarky and building millions of bunkers could help his country survive the inevitable invasion.
In short, the most common way it presents is the nationwide equivalent of prepping.
While energy independence — something you hear cited as justification for both expanding renewable energy and drilling for oil in the Alaskan wildlife reserves — is indeed an important, if not the most important, component of autarky, it is not the same and the aims are different. While autarky takes "dependence" on foreign trade as bad per se and tries to replace imported resources and goods with domestically produced things even if they are clearly inferior, energy independence allows a country to be strategically and economically independent of a handful of large suppliers. In theory, a similar effect to energy independence could also be reached by diversifying the countries from which energy resources are bought. However, this is usually impossible as long as energy relies on oil to a measurable degree, as oil is largely in the hand of a few countries.
One particular recurring trend in modern autarky attempts is coal liquefaction, as many countries have abundant coal reserves but only a few countries have significant oil resources.