Margaret Thatcher has been important in the history of the world for two main reasons. One has to do with the Cold War and the other has to do with England in particular.
Thatcher was also important for other reasons. She was the first female prime minister of England. She led the country in its war against Argentina over the Falkland Islands. These things alone would have made her famous. However, she is even more important for two other reasons.
First, Thatcher, along with Ronald Reagan, was a firmly anti-communist figure in the last decade of the Cold War. Thatcher helped to ensure that the second most important country in the West was strongly anti-communist during the 1980s. This helped to put pressure on the Soviet Union and can be said to have helped to end the Cold War.
Second, Thatcher turned England’s economy around. Until she became prime minister, England was relatively poor. Its government was very involved in the economy with many important industries being under government control. Thatcher pushed hard for liberalization of the economy. She pushed to get the government to be less involved and to make more of a free market economy. These changes profoundly transformed England, which is why the reactions to her death earlier this year were so divided and so passionate.