As you know, Sailor Moon's clothes are based on Japanese girls' middle-school and high-school uniforms called sailor fuku (sailor suits).
Here is some information I hope people are interested by.
At the bottom are some fun links.
In Japan, people will recall at first female students, especially of the ages for junior high schools or high schools when they hear the word "sailor".
Because in Japan, the sailor suits (or middies) are introduced as uniforms of some schools.
Why the sailor suit was used as an uniform for the girl student?
The history began at the beginning of the 17 century in Europe.
In those days, the sailor suit was made, of course, for sailors.
Especially in 1628, the Great Britain Navy introduced the suit as an uniform.
I omit to write the reasons.
In 1840's, the sailor suit was in fashion for little boys.
The beginning was a photograph of the prince Edward, (EDWARD VII subsequently) 5 years old in the sailor suit.
And with its pretty design, there was a run on the suit for all children and also for females.
It was also in Europe, after 1910's.
You can see many photos at that time of children in sailor suits.
At the same time, Japan was in the era of TAISHO, and the democracy began to bloom.
Especially the women's status in society was just a little improved.
They stopped to wear the typical old japanese clothes(KIMONO), which was a symbol of old bad tradition, and many girl schools introduced the sailor suit as an uniform because of the vogue in Europe.
I also omit here the recent situation in japan, but at least, the image of the sailor suit is still deeply related to the image of young girls.