When a government takes ownership of a private-sector business. Nationalization was a fashionable part of the mix in countries with a mixed economy between 1945 and 1980, after which the privatization of state-owned firms became increasingly popular. The amount of public ownership in different countries has always varied considerably. Nationalization has taken place for various reasons, ranging from socialist ideology to attempts to remedy examples of market failure. The performance of nationalized firms has often, but not always, been poor compared with their private-sector counterparts. State-owned businesses often enjoy a legally protected monopoly, and the lack of competition means the firms face little pressure to be efficient. Politicians often interfere in important management decisions, making it harder to take unpopular actions on pay, factory closures and job cuts, particularly when there are strong public-sector trade unions and a union-friendly government. Politically imposed financial constraints may also force public-sector firms to underinvest. Although privatization has not been universally beneficial, on balance it has increased economic efficiency.