Hypothetical situation: The collapse of the International Money Market.
Greece and Ireland's dire economic situation drag the other European countries down with them, soon other nations gain massive deficits, starting with the smaller Balkans countries and moving up to France, Italy, and Spain.
Germany just about manages to hold on, because of their high levels of industry and by quitting the Euro just in time and establishing a new currency (The Hasslehoff)
The U.K. hastily leave the E.U. and just manage to stay afloat with their pounds sterling... For now.
The Euro collapses. This leaves most European countries without a proper currency, and most regress to bartering systems. Several countries become police states in order to keep the peace. The Scandanavian countries fair extremely well, bartering their excess power from the renewable energy sources for food and luxuries, Russia and the Middle Eastern countries also earn great profits from their fossil fuel sources.
The American and Japanese stock markets, while declining steadily during this strife, take a massive nose dive due to the fall of the Euro, and this heralds America to begin forcing the collection of debt repayments from various countries that they have lent money to. (mainly African nations) This stabilises the dollar... for about a month. Then China and Japan demand repayment of their debt, the Uk gets in on the deal later, and America is quickly bankrupted, the economy moves back to the gold standard, and the rich/poor margin skyrockets. American public outcry and riots force America to deploy their own army against the rioters, and, backed by the weapons, the politicians quickly change the constitution to ensure they have more power and the people less freedom. America becomes a police state.
China and Japan have become extremely rich due to the American money. China uses it's superior numbers and advanced military tech to immediately invades Japan and homogenises their wealth. North Korea, lead by Kim Jong Un, decides to attack China to take over their power, and after a very bloody war lasting about 6 months, North Korea is defeated and homogenised by China. South Korea piddles its pants, and quickly signs a trade agreement with China.
Africa is ravaged by disease, drought, and war and doesn't have any international help. South America fairs much better, most people move back to subsistance farming, and the Rainforest is cut up mercilessly for farmland and fuel.
The Western countries almost regress to their state during the industrial revolution. Factories are once again all over cities, mass producing goods to be export cheaply to the decadent Middle East (what a turn around!) and with food prices skyrocketing farming is incredibly lucrative. Virtually all Europes forests are systematically cut down to grow crops, which are rarely exported.
Canada's large amount of natural resources and connection to the UK meant they have survived quite well, exporting their highly desirable wares to the USA. Unfortunately this also makes them a highly desirable target. After a tense military buildup on both sides (with the UK bringing their military forces in) the USA invades Canada, but although they have clear aerial superiority and are able to lay waste to many of Canada's cities, their ground troops are hampered by the terrain and weather, and forced into a stalemate. America tries to nuke Toronto but the missiles are destroyed mid-flight. British nuclear submarines travel to within the range of Washington DC and an uneasy truce is agreed. America withdraws, invades and conquers Mexico.
And that's what will happen over the next 20 years. Remember, you heard it here first folks!
