(Mental Floss) -- Over the centuries, people have had some very good reasons to dress up like a member of the opposite sex. 

And I'm not talking about people who live this way out of personal preference, or those who dress up for theater and entertainment. 

Here are just five examples. 

1. Cross-dressing to join the army 

Until recently, women have rarely been allowed to serve as soldiers. 

So what was a gal to do if she wanted to serve her country? Naturally, disguise herself as a man and join the troops. 

At least 400 Civil War soldiers were women in drag. These included Union Army soldier "Frank Thompson" (also known as Sarah Edmonds), whose small frame and feminine mannerisms (rather than causing suspicion) made her an ideal spy, as she could spy on the Confederates disguised as... a woman! 

She wasn't the first woman to don a male disguise and join the army, though. During the Revolutionary War, women fought as men on both sides. 

Hannah Snell, for example, joined the British army to find her husband, who had walked out on her to enlist. 

Once her true sex was discovered (thanks to a pesky groin injury), she became a national celebrity in Britain, and made a post-war career of performing in bars as the "Female Warrior." Mental Floss: The Confederacy's plan to conquer Latin America 

2. Cross-dressing to keep a royal family together 

With all the power play that went on in the court, the French royal family would go to great lengths to avoid sibling rivalry. In one of the more extreme cases, Philippe I, Duke of Orleans (1640-1701), was raised as a girl to discourage him from any political or military aspirations. 
What type of competition was being avoided?
 great lengths to avoid sibling rivalry