In democratic countries, I'd say generally that's because of the failure of the people. Even if they (just for thought experiment) manage to buy ministers, a president, etc., from the best country, not necessarily the mentioned country will be prosperous.
To be more precise, lots of falls in the economy were caused by corruption, wars, and lack of risk management. Therefore, people need to check what the government is doing and be more proactive.
https://www.investopedia.com/articles/economics/08/past-recessions.aspEach citizen who already has the right to vote should use his vote in the election. If someone has high ideals and are confident that s/he can make positive changes there is no harm for the millennial generation in politics, only if s/he has entered politics should not be carried away by the current corrupt and oligarchic practices that are common in politics.
We must have clear knowledge and data about what the government is doing so that we can get involved in policy formulation. Eliminate the assumption that politics is just the opposite, we must understand politics and government in order to contribute.
Bad government is the other side of the coin when it comes to the fate of a country's economy in my opinion, the other side would be the people of the said country, the population in China is not just an employment thing, the other thing about it is the consumer base is so large, companies are vying to get their hands in Chinese soil which in turn makes tax that helps in government funding and spending. We also should consider the GDP of a country because they serve as an indicator whether they are prospering or not. War in my opinion is just an off shoot of bad government.
Whatever happens in a country, especially in large countries depends on how the government, especially the head of state, governs a country. Although the national interests are the same (the grand plan remains unchanged), different leaders differ in strategy and policy. Take for example the era of Obama and Clinton, the United States is very close to China. Unlike when Trump's era, China became an opponent, not a strategic partner.
Likewise, China under Deng Xiaoping and under Xi Jing Ping has a very different foreign policy. Under Deng, a Chinese reformer opened himself up to bring about rapid development in China. While Xi is an innovator who initiated the China Dream or the Great Revival of the Chinese Nation, to restore the glory of China, namely the one belt one road program.
Natural resources and human resources in a country can be a bonus that can be disastrous depending on the ability of the government in the state and managing all potential bonuses and potential disasters that exist in the country. Almost all countries are based on laws and constitutions in force in those countries. One of the strengths of leaders is that the decisions chosen are legally recognized and are binding on all citizens. So the leader remains a determining factor for the progress or setback of a country.