(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. 
Were women always allowed in the military?
How could a women participate, despite the regulations against it?
During which war did this happen?
Was it limited to only one side of the conflict?
What name did Sarah Edmonds use to enlist?
In what war did she fight?
How many other women joined her?
Sarah's statue made her an ideal candidate for what position?
Why did Hannah Snell join the army?
Which army had he joined?
Did Hannah become famous?
How was she caught?
Where did she perform?
As what character?
Which royal family member was raised as a member of the opposite sex?
When did he live?
What did his family want to discourage him from?
What type of competition was being avoided?
In what country did Hannah Snell become famous after her discharge?
no
Until recently, women have rarely been allowed to serve as soldiers.
disguise herself as a man
Naturally, disguise herself as a man
Revolutionary War
During the Revolutionary War, women fought as men on both sides.
no
women fought as men on both sides. 
Frank Thompson
 "Frank Thompson" (also known as Sarah Edmonds)
Civil War
At least 400 Civil War soldiers were women in drag. These included Union Army soldier "Frank Thompson
At least 400
At least 400 Civil War soldiers
a spy
also known as Sarah Edmonds), whose small frame and feminine mannerisms (rather than causing suspicion) made her an ideal spy
to find her husband
Hannah Snell, for example, joined the British army to find her husband
the British army
Hannah Snell, for example, joined the British arm
yes
Once her true sex was discovered (thanks to a pesky groin injury), she became a national celebrity in Britain
a groin injury
Once her true sex was discovered (thanks to a pesky groin injury)
bars
and made a post-war career of performing in bars
the "Female Warrior"
as the "Female Warrior."
Philippe I
In one of the more extreme cases, Philippe I, Duke of Orleans (1640-1701), was raised as a girl 
1640-1701
Philippe I, Duke of Orleans (1640-1701)
political or military aspirations
 to discourage him from any political or military aspirations.
sibling rivalry
 great lengths to avoid sibling rivalry
Britain
a national celebrity in Britain