That's a tough question to answer in a short message! :-)

It depends on the constitution of the country. In the UK we have a constitutional monarchy, so we don't have a President as head of state because we have the Queen.

Just some corrections...

<em>Why don't some countries have a president?</em>

<em>Why isn't there a president in some countries?</em>

Well, different countries have different histories and political systems. I'm not sure whether a president is mandatory.

Some countries have a king and queen, for example: UK, Spain. Other countries have Prime Minister. Chile has not it because it has a presidential system.

History, culture, and historical accident. A "president" is "The chief executive of a republic." So, why isn't every country a republic? Well, different countries just have different systems of government, and that's all you can say.

Due to heritage, many countries have governments that are patterned on other countries' governments, and tend to use the same terminology. If a country has something called a "parliament," it will probably have an official called a "prime minister" or a "premier" rather than a "president."

Wikipedia has an interesting article: https://en.wikipedia.org/wiki/Presidential_system

"A presidential system is a republican system of government where a head of government is also head of state and leads an executive branch that is separate from the legislative branch. The United States, for instance, has a presidential system. The executive is elected and often titled 'president' and is not responsible to the legislature and cannot, in normal circumstances, dismiss it."

Thank you teacher Peachey