Brushing up on a little history of the period when your ancestors lived can save you hours of digging for clues that may not even exist because history has already determined precisely what sort of government documented information is available. It's good for you to know the types of information collected, the year it was collected, and the locations.
Take the Battle of the Wabash River, for example. This somewhat obscure battle in 1791 between Native Americans and U.S. troops under the lead of Major General Arthur St. Clair, which took place on a branch of the Wabash River in what's now Ohio, is infamous for being the most severe defeat ever suffered by the US Government at the hands of Native American warriors, led by Miami Chief Little Turtle and Shawnee Chief Blue Jacket. Of the 1,000 US troops, only 48 survived.
Although this battle isn't everyday historical knowledge for the average person, what happened may be important to your genealogical search. The soldiers and Native Americans who died in battle that day were someone's ancestors–perhaps yours. Their deaths may have caused shifts and voids in ancestral lines in many families over time. So the first question you'd need to ask yourself is does the U.S. Government have records on the dead soldiers? As members of the military, you bet it does. Unfortunately, the same cannot be said for their Native American counterparts who most likely didn't have any written history at the time.
Many beginning genealogists only consider the main events in history and not the smaller, more inconsequential ones. Major-war casualty lists from the Revolutionary and Civil War have long been sources for genealogical searches. But nearly all battles and skirmished throughout our history have been documented by the men who led them and are part of our national archives. If you found your ancestor had joined the U.S. Army and had disappeared in 1873, wouldn't this piece of history concern you?
Suppose you were having difficulty locating an ancestor in western Pennsylvania. According to the census of 1880, that person owned a farm near Johnstown. But you can't find any proof of his death in the Pennsylvania state death records. The person literally disappeared in 1889.
On May 31 of that year, the Great Flood of 1889 struck not only Johnstown but the entire river valley 14 miles north of the city. It was the result of the collapse of the South Fork Dam, caused by nearly a week of extremely heavy rainfall. Sure, there were warnings of the dam's failure, but many people ignored them because they had heard them many times before. When the dam finally broke, it unleashed a torrent of 20 million gallons of water that swept down the valley taking 2,200 people to their deaths. If your ancestor was a farmer, it's very likely that he lived somewhere along the path of the flood. Many people were never found and hundreds of others were burned in a massive fire when a jam up occurred at the Pennsylvania Railroad viaduct.
If your ancestors vanished in New York City in 1866, perhaps the reason was the outbreak of Cholera, brought in by Russian immigrants, that killed 2,000 people. Authorities, trying to control the spread of the disease, ordered that victims bodies be burned and buried in lye in mass graves. They also burned their homes and belongings
Before you begin any genealogical search, take a look a the greater historical picture. Check the historical index of any almanac for the time period in which your ancestor lived. Look at the events, then study the history of those events and try to figure out if your ancestor may have been affected.
If you find no clues or traces left of an ancestor, that may indicate a natural or man-made catastrophe. Perhaps it was something simpler, like the vandalizing of a gravestone. Perhaps old unprotected records burned in a fire. When you're investigating lost ancestors, the odds are against you from the beginning if your ancestors were poor, ethnic, rural, or lost in a catastrophe.
A good genealogist is like a good detective. He or she never gives up, always hoping there's that one tiny, overlooked clue lurking somewhere–a key that will unlock the door to the past.