International Relations/International Realism Theory
A main argument of realist theory is that states (or nations) are always engaged in a struggle for power. One of the earliest books to espouse Realist theory is Machiavelli's The Prince, which was written for the de Medici family as a guide to uniting Italy. A later, more comprehensive book that helped build the foundation of Realist theory was "Politics Among Nations", by Hans J. Morgenthau.
Realist theory advocates the use of power to fulfill the interest of a nation. "National power" is composed of geography, economy and natural resources, population, military strength and preparedness, national character and moral, and the competency of the national government.
The influence of geography can be broken down into the separation of nations and the size of nations. Nations can be separated by deserts, mountains, rivers, and, most notably, oceans. Deserts prevented Egypt, Greece, and Rome from establishing contact with the parts of Africa south of the Sahara and prevented the Aztecs from contacting Indians in the modern United States. Though they rarely destroy a powerful army, deserts often wear the army down and help its eventual destruction. The power of mountains is illustrated by the Alps, which prevented Rome from effectively controlling modern-day France and Germany. The power of water is twofold; military power and trade/economic power. It is no accident that the two most recent superpowers, Britain and the United States, are isolated from rivals by oceans. Armies can only cross water when it is bridged; rivers can be bridged, oceans cannot. Thus, both Britain and the US have been protected from foreign armies by water, and need only to maintain a navy to ensure that enemy troops cannot be transported by boat.
Water also provides fast, easy, cheap, and large-scale transportation. It is no accident that the two most economically powerful cities in the world, New York and Hong Kong, are on river deltas. Not only does this transportation benefit industry, but it can also allow troops to be moved in large numbers (and they will not be tired when their journey is over), but it also allows a nation to watch over its interest with a navy, as both Britain and the US have done. The size of a nation works much like natural barriers. However, rather than an army being unable to cross a certain barrier, a large nation may have too much land for the army to cross. Russia used this advantage when it was invaded by Napoleon and Hitler, and had success when wearing the enemy down, rather than facing it head-on (wearing the enemy down is usually termed attrition). A large landmass also gives a nation better chance of having ample natural resources. This is not to say that small nations are weak, it is often the opposite. Though Britain has depended on food imports for well over 100 years, it upheld considerable power until the end of WWII, and the Netherlands have been, and still are, a notable economic power. Further, the Papal States is arguably the most influential nation, per capita, on Earth, though its military power is subject to much speculation.
It is the economy of a nation that supports the creation of a military. A modern economy can build modern equipment for a military, while a large economy can build massive amounts of equipment and supply more troops.
There are 3 ways in which economies are used in national competition: military Vs. economy, sustainable military Vs. overstretched military, and economy Vs. economy.
The first situation is when nation A uses its military to attack the economy of nation B. Examples of this are naval blockades (which prevent trade) and the destruction or capture of cities or vital infrastructure. These tactics were used notably in WWII with varying success. In order to conduct a successful naval blockade, there are three things to analyze: the strength of your navy compared to the enemy navy, the enemy's dependence on imports by sea (and if those imports can be redirected to a land route), and the potential reactions of those who will no longer be able to trade with the blockaded. The first aspect is illustrated in the mutual blockades of Britain and Germany during both World Wars. Britain had the more powerful navy, and though German U-boats made Britain pay dearly for its supplies, the more powerful navy eventually won the rivaling embargoes. The second consideration is illustrated in Napoleon's embargo on Britain. Though Britain did suffer from the embargo, it did not depend on mainland Europe for supplies, and was able to survive with the help of its colonies. The third aspect is exemplified by the German attack on the Lusitania, which pushed America to enter WWI and helped tip the scales in favor of Britain and France.
The second possibility, sustainable military Vs. overstretched military, is not a conflict of the militaries themselves, but rather a struggle of two nations to sustain their respectful militaries. In this case, the overstretched (or oversized) military, like those of Napoleon and Hitler when invading Russia, eventually crumbled because the militaries could not be maintained by the nation. Additionally, much of the Cold War falls into this category.
Finally, economy vs. economy competitions are seen in international trade, tariffs, and embargoes. If nation A wants to destroy a certain part of nation B's economy, nation A can flood nation B with products at an extremely low price, and eventually destroy the companies in nation B which cannot compete with nation A's far cheaper products. The effects of such an action are twofold; nation B depends on nation A for that product, and nation A can raise prices as competition has vanished; also, nation B is deprived of a product that may be important to the nation's security, and thus is weaker if nation A and nation B go to war. Protective tariffs are designed to prevent actions such as this. Protective tariffs are an extra tax on certain, or all, products, thus preventing nation A from flooding nation B's economy, as nation A's products are no longer cheaper, as they have to pay the extra tax. Additionally, protective taxes can be used to help build a new or small industry, not just protect one that is at risk. Not all tariffs are protective, many are used only to raise revenues for national governments, but all tariffs have financial and protective effects. Finally, embargoes are very similar to blockades, but the embargoing nation threatens to impose trade restriction on those who trade with the embargoed, rather than use military force. This method is not as effective as blockades – there is nothing to prevent nations that are already embargoed from trading with each other – but it is useful for compelling a nation to follow the wishes of the embargoing, and can also be used as a predecessor to blockades if a war is to break out.