There are two versions how the French Defence got it's name:
1.) A correspondence chess game between the club Cercle de Philidor of Paris and the Westminster Chess Club in London beginning in 1834.
The first moves were ( with Paris playing as black) :
1.e4 e6 2.d4 d5 3.exd5 exd5 4.Nf3 Nf6 5.Bd3 c5 ( quite a modern approach to play the Exchange variation of the French Defence ! )
The French sent a challenge to Westminster Chess Club in January 1834 and they accepted. Each side entered 50 pounds and London mailed the first move in February 1834. The French were led by Pierre de Saint Amant and went on to win in 27 moves in 1836. After that game the name French Defence was given, as Paris won the game
2.) Geza Maroczy mentions in his book "Die Französische Partie" from 1927 that Carl Friedrich von Jaenisch published in 1842 a monograph about the opening and because he was living at this time in Paris it was called "The French Defence".
At these times the French Defence (as the Sicilian Defence, etc.) was seen as an exotic alternative to the "normal" 1.-e5 open games. The Opening Encyclopedia of this time was "The Bilguer" and in the 1843 edition the French and the Sicilian Defence have together less than 40 pages compared to about 300 pages about the open games openings. And for the French Defence only 3.exd5 and 3.e5 are mentioned.
Only slowly then was the development of the theory of the French Defence. Luis Paulsen introduced 3.Nc3 and Siegbert Tarrasch 3.Nd2.
Around 1900 the French Defence was established on Master level.
Great contributions to the theory of the French Defence later made Aaron Nimzowitsch and Mikhail Botvinnik. After 1945 especially Russian players developed the French Defence theory further. Acording to Megabase now the French Defence is No.3 of the popular defences to 1.e4.
Securing a space advantage and hindering black's kingside development. Black will attack white's pawn chain c3-d4-e5 with c5 / f6 and the question is if white can support, or black destroy it.
White defends his e4 pawn with the knight without allowing the pin Bb4. Black's main lines are now 3.-c5 (attacking the center) and 3.-Nf6 (attacking the e4 pawn again). Alternatives are 3.-a6, 3.-Be7 or 3.-Nc6.
|C00 (Early Deviations)||This is an overview of all the theory presented||C10 (Rubinstein Variation)|
|C01 (Exchange Variation)||here at Chessfriend.com||C11 ( 3.Nc3 Nf6 Steinitz Variation)|
|C02 (Advance Variation)||C12 (3.Nc3 Nf6 4.Bg5 Bb4 McCutcheon Variation)|
|C03 (3.Nd2 Be7)||C13 (3.Nc3 Nf6 4.Bg5 dxe4 Burn Variation)|
|C04 (Guimard Variation)||C14 ( 3.Nc3 Nf6 4.Bg5 Be7)|
|C05 (3.Nd2 Nf6)||C15 (3.Nc3 Bb4 Winawer Variation)|
|C06 (3.Nd2 Nf6 4.e5 Nfd7 5.Bd3)||C16 (3.Nc3 Bb4 4.e5)|
|C07 (3.Nd2 c5 4.exd5 Qxd5)||C17 (3.Nc3 Bb4 4.e5 c5)|
|C08 ( 3.Nd2 c5 4.exd5 exd5)||C18 (3.Nc3 Bb4 4.e5 c5 5.a3)|
|C09 ( 3.Nd2 c5 4.exd5 exd5 5.Ngf3 Nc6)||C19 (3.Nc3 Bb4 4 e5 c5 5.a3 Bxc3+ 6.bxc3 Ne7 7.Nf3 and 7.a4)|
White defending pawn e4 by Nc3. ( If Black then takes on e4 we have the Rubinstein French). And Black attacking the pawn again by developing a piece with Nf6. Now White has several options to react.
A more aggresive move in order to attack the pawn e4. Black is pinning the White Knight on c3 and is now threatening to take the pawn on e4. Doing so he must be willing to exchange his Bb4 for the Nc3.