What has been the most common reason for one-party losing control the national government

In the electoral history of  the US and other democratic countries, except for unusual circumstances or events, the economy is the main concern of voters. People are more concerned about having jobs, getting incomes to raise kids and keep families, having the possibility of buying a home, and so on. Normally, people are less worried about events in foreign countries.  

Explanation:

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length of the cultivating season was not a problem of new england agriculture