The most burning questions every family historian asks always begin with why.

As genealogists, we primarily seek out definitive evidence that an event happened, but rarely do we understand why something happened by just looking at a census or vital record.

Researching your family in the US census is bound to raise a lot of why's, especially regarding geography. Thanks to the census, you can draw precise information about where your family lived every in nearly every one. There's really no other source like it - it was done without fail every 10 years since 1790.

If you extract all of the information you can out of censuses, the major difference you will notice between decades is where your family lived. Of course some families have stayed put throughout their history, but the vast majority have moved quite a few times.

With diligence, you should be able to use the US census to plot out your family's location on a map throughout history. Whenever you encounter a change of residence, you can't help but wonder why your family picked up and moved.

While it may be impossible to determine the exact reason with confidence, many families were part of larger mass migrations in history - their move could have been triggered by a major historical event, or they could be participants in a historical trend that you learned about in school.

Wouldn't it be interesting to know?

Let's take a look at two possible reasons reasons for mass migration and provide a few examples from history.

Freezing crops

In many cases, it's reasonable to assume our ancestors didn't really want to move. But economic or climate disaster (often paired hand-in-hand) often forced the migration of many people throughout history.

America has been a nation of agriculture since the earliest settlers, which undoubtedly benefited our ancestors. But such reliance on the yearly crop yield also means reliance on the kindness of mother nature - hardly ever a guarantee.

This map shows the frigid temperatures across Europe. North America suffered badly as well, especially the northeast.

An interesting example is the Year Without Summer - in 1816, the world suffered a catastrophic drop in average temperatures, creating what historians refer to as "the last great subsistence crisis of the Western world."

Temperatures fluctuated wildly that year. In New England, temperatures dropped below freezing in May, June, July and August, killing a huge number of crops. A mysterious dry red fog hug over much of the area as well.

This caused a scarcity of grain and caused the price of bread to increase over 700% in some locations. Many poor risked starvation. As those in high altitudes were especially affected by the colds, people began to move to lower more stable climates.

An estimated 10,000 to 15,000 people emigrated from Vermont alone. Many of them settled in western New York and Pennsylvania. Other locations of New England saw a huge exodus as well. If your ancestors moved in 1816, this could definitely be part of the reason!

Read more about the Year Without Summer

The Dust Bowl

The Dust Bowl was another economic and natural disaster that caused a mass migration.Library of Congress, Prints & Photographs Division

One thing every family researcher needs to do is compare notes between the 1920, 1930 and 1940 census to see how the Great Depression affected your family. Many people moved for all sorts of reasons during the depression - there were few families that weren't affected.

But if you had family who were Midwestern farmers, they were undoubtedly affected by the Dust Bowl. In short, the Great Plains was blessed by a period of uncharacteristically friendly weather in the several decades before 1930. Farmers mistakenly believed this would last forever.

Read more - 1939: The year the dust settled

A series of massive droughts hit the Great Plains in the early 1930's, causing entire farms to erode and turn to nothing bust dust.

An estimated 500,000 people lost their homes due to the Dust Bowl, and by 1939 3.5 million people in total had left the Midwest. Although they came from all plains states, they were known as "Okies" - the majority settled in California. Over 86,000 people immigrated to the Golden State in a one year period.

Bonus tip: The 1940 census has a special field asking where the family lived in 1935. With that, you'll be able to track your family at 5-year intervals during the depression to get an even better idea of their movement.

All US Federal censuses are free on Findmypast

These are only a couple of the many climate disasters and changes that cause migration in American history. How can you form a hypothesis about the reason for their move? Read your history!

Pinpoint the approximate time of their move and search for major events that happened in their area. Search newspapers, PERSI or even Wikipedia and you may be surprised that what you find fits logically with their story.

Of course it's important to remember that you need some hard proof to definitively conclude why something happened. It's perfectly okay to use words like likely or possibly when explaining the why of a location change.

Learn more about the census