Networks in Europa Universalis IV
http://www.eu4wiki.com/Diplomacy
The video game Europa Universalis IV aims to allow the player to create an alternate history starting in 1444 and ending in 1821. The player guides a country through this 400 year period, along the way making decisions such as which other nations to ally or attack, where to colonize, and how to develop his or her nation. In order to accurately simulate international diplomacy, the game’s AI uses a system that represents each country’s opinion of other countries as an integer from -200 to 200. The lower their opinion, the more they dislike a country, the higher their opinion, the more friendly they are. These opinions directly affect a country’s actions towards its fellow nations; a country that has a strongly negative opinion of another is more likely to attack it, while it is more likely to desire an alliance or trade agreement with a country of whom it has a positive opinion. These are equivalent to the positive and negative edges of a graph that we studied in class.
More interesting than this is that the game automatically forms balanced networks, even though the AI is not explicitly coded to do so. The network balancing arises naturally from these opinion modifiers. Each country is allowed to choose three rivals, nations with whom they receive a large opinion decrease. They also receive numerous benefits for taking hostile actions towards these rival nations. They are also programmed to receive opinion bonuses with countries with whom they share rivals; it is quite common to see, for example, France and Spain forming an alliance to fight against their mutual rival England, an example of a +,-,- triangle. On the contrary, countries receive opinion penalties towards countries allied with their rivals, so they tend to resist the formation of +,+,- triangles. Alliances with these nations will only occur if the benefit to the country would vastly outweigh this negative, and usually are very short lived.
By the end of the game, the countries almost always sort themselves into two major blocks, in which all countries on one side are friends and/or allies, and are enemies/rivals of all countries in the other block, much like we discussed in class. This will often lead to a world war-like scenario occurring 150 years or so early.