Political change can either increase or decrease a country's attractiveness for tourism, depending on what the change is. If a country is perceived as unsafe before the change and the change results in a feeling of increased stability, then the country can slowly recover to a natural state of tourism. But if the country is perceived as unstable as a result of the political change, such as is the case now with Egypt, tourism will plummet.
The type and severity of the effect obviously depends on what type of political change has occurred in a country. As others have mentioned, Egypt and several other countries in the region are undergoing political turmoil right now. Americans and other foreigners currently in the country have had significant difficulty getting out and ATM machines have been emptied in many areas of the country. While this turmoil hopefully will not last, it will discourage many from traveling there--a country that depends heavily on the tourism industry.
From a positive standpoint, countries that were once isolated by the Iron Curtain, have enjoyed a rise in tourism since the fall of the Soviet Union. I took students on a trip to the Czech Republic several years ago, and while it was obvious that the country was still struggling to growing accustomed to their new-found freedom, it was also evident, that cities such as Prague were benefiting greatly from the tourism industry.
There is no doubt that political unrest will cause people to think twice about being a tourist in a country. All the posts above give great examples of current situations to back that up. I also think though that change for the better in the political climate of a country can cause an increase in tourism.
There have been a variety of examples given. Another is Thailand, which reportedly lost a great deal of tourist money in its recent protests, especially after the airport was taken over.
Politically unstable conditions can result in a public reluctance to travel to a country, or a government warning of danger as a result of political strife. You might consult a government bureau of travel for more information.
You might want to add countries like Zimbabwe to that list. Also, I fear that people might be scared to book a beach holiday on Sumatra or Java in Indonesia where they have suffered recent tsunamis. Unfortunately, as these and other cases listed above show, factors beyond the tourist industries control have a massive impact on the tourist industry of a country.
I doubt that many people have been booking hotels and tours in Tunisia or Egypt at the moment, as even the appearance of instability or unrest tends to seriously discourage peoples' travel plans to a region. Mexico is another great example, as the other poster mentions.
As for Germany, as post #4 brings up, I only know that in 1989, I sold my Chevy Nova, bought a plane ticket to Berlin and drank champagne with two West Berliners as we took turns swinging a sledgehammer at a graffiti caricature of Nikita Khruschev. So I guess at the least it stimulated the airline industry, the champagne industry, and the sledgehammer industry.
Both great examples of how an unstable political environment can affect tourism. I'm wondering, however, if there can be positive change. Think about the reunification of Germany. I wonder what that might have done for tourism?
Let's take a look at Mexico right now. The current President has taken a stand on the drug trade and it has increased the violence between the military/police and the drug distributors. It used to be that the politicians and police were all tipped off to look the other way. Part of the reason for the violence has to do with the enforcement becoming more stringent. This impacts tourism to Mexico dramatically right now. Because of this political unrest and apparent danger, Americans are not frequenting Mexico's resort communities in the mass numbers that they used too. Mexico's economy will suffer as a result.
Political change in a country can seriously impact the prospects for the tourism industry in that country. Radical changes in a countries politics can cause tourists to fear for their safety and, therefore, avoid a country. Recently, Thailand (which has various popular beach resorts) has had political unrest which, at one point, extended to the occupation of the airport in its capital. This sort of political change is likely to have negative impacts on the tourism industry.
Political change in the tourists' home country can also have an impact on the tourism industry. Perhaps the best example of this right now would be Cuba. The restrictions on travel by US citizens to Cuba seriously reduces the prospects for that country's tourism industry.
Well, lets look at the massive riots in Egypt today. When such events occur tourism comes to a halt.