Anything that can threaten your survival is an enemy, whether it is hunger, disease, harsh natural environment, or violence. While many solutions exist, there is an economic component that exists with many of them.
Consider hunger, a man who lives in a rural area can fight it through picking berries in a forest, or growing plants on his property and eating those. In this example the man who decides to farm is more likely to survive then the man picking berries. Both berry picking and farming requires preparation, but farming requires more preparation than picking. If a man is hunting in order to fight hunger the man who brings a gun is going to be more prepared than the man who brought a spear. The more you are prepared to fight hunger, the more likely you are to survive.

Disease is another enemy of humanity, which can be fought either alone, or with help. Man can take certain precautions in order to fight off disease by avoiding those already sick, exercising, eating right, etc. in order to be prepared against certain diseases. Some diseases will get to you despite these precautions and can only be fought using modern medicine. But if you are prepared and have a doctor ready, medications, and are actively fighting the disease, you stand a much higher chance of surviving then if you ignored all these preparations.
Nature kills thousands who fail to prepare for it leading to deaths due to extreme hots and colds. Shelter can be used to protect oneself from the harshness of nature, from the Native Americans who used tents, New Guineans who live in huts, the New Yorker who lives in his apartment, or the businessman who resides in his mansion, all of these things, while including luxury, are based upon protection from nature.

While all the previous enemies could be solved rationally, the one remaining enemy, violence, can only be solved by using violence or the threat of violence. In the case where someone is trying to kill you, its rarely a matter of being able to negotiate with your assailant, as in these situations someone is most likely going to die, the only question is will it be you, or the murderer? When we are trying to protect ourselves against other humans, most people rely on their local police to save them in a time of crisis, rather than prepare themselves by arming themselves. If whoever is trying to kill you takes longer than 10-20 minutes to get to you, then the police can protect you! But if, like most cases, he can kill in you around 3 minutes, then what good are the police besides a clean up crew? On the other hand, the man who arms himself is doing nothing more than preparing for whatever types of violence may come his way, and he will be more likely to survive than the man who relies on the police.
The threat of violence goes beyond a personal level, but also includes international threats that wish to take over your home country by force. There are two main ways of preparation against this threat, an army, or treaties. While an army works all the time, a treaty is only as good as the character of the country. In 1991 the Soviet Union dissolved, leaving in its inheritance over 4,000 nuclear warheads in the hands of the new Ukrainian government. Ukraine had every intention of keeping this world’s third largest nuclear armada to protect itself from any aggressors, but in 1994 it was pressured into signing a treaty that gave all its nuclear arms back to Russia, in exchange for a pledge from both the U.S. and Russia that they would never threaten Ukraine’s territory. Jump ahead 20 years later, and we see Russia sending forces into Crimea and putting it under Russian control. Ukraine only ever signed that treaty in 1994 because the U.S. at the time was a respectable nation; it thought that it did not need to prepare itself against any sort of invasion. Now it is realizing its mistake, if Ukraine had kept its massive nuclear armada, there is not way Russia would have ever threatened Crimea.
In all these examples I have ignored the more modern method of dealing with these enemies, which simply put is trade. When we work we are rewarded with a currency that lets us trade our work for things we need. To solve hunger we buy groceries. To solve sickness we buy insurance or pay doctors directly. To solve shelter we promise banks to reward them with extra money (interest) in exchange for covering the purchase of a home. To solve violence we pay taxes with the promise that police will help. (Some of us are allowed to subsidize these efforts with the purchase of weapons we could never manufacture on our own.) But this brings up a new consideration. Economics becomes critical to our survival when we use economic means to defeat these enemies.
Any economically run culture also faces a unique enemy, one of economic chaos. When un-payable debt on a international scale results in hyper-inflation, the currency of work and trade becomes useless, making everyone who for their protection suddenly vulnerable. When a currency collapses, survival at a basic level becomes the new norm, the chemist must learn to hunt, the judge must learn to farm, and the doctor must learn to fish. People of American society generally don’t practice professions that teach survival, they instead study law, teaching, mathematics, etc. all of which would serve no practical purpose without the possibility of trade. Proper preparation meaning educating yourself on which politicians are frugal, against those who use the nation’s wealth to buy themselves votes thru wasteful spending and crony-capitalism. Without a cautious approach to politics, a nation and its people must live in the shadow of facing destruction that most modern people cannot fathom.

While most people focus on our more direct enemies, being hunger, disease etc. few bother to realize that our solution, economics, could become our greatest enemy.