On résiste à l'invasion des armées; on ne résiste pas à l'invasion des idées.
One resists the invasion of armies; one does not resist the invasion of ideas.
One withstands the invasion of armies; one does not withstand the invasion of ideas.
Histoire d'un Crime (The History of a Crime) [written 1852, published 1877], Conclusion, ch. X. Trans. T.H. Joyce and Arthur Locker http://fr.wikisource.org/wiki/Histoire_d%E2%80%99un_crime_-_Conclusion#X.
Alternative translations and paraphrased variants:
One cannot resist an idea whose time has come.
No one can resist an idea whose time has come.
Nothing is stronger than an idea whose time has come.
Armies cannot stop an idea whose time has come.
No army can stop an idea whose time has come.
Nothing is as powerful as an idea whose time has come.
There is one thing stronger than all the armies in the world, and that is an idea whose time has come.
Many of these paraphrases have a closer match in a passage from Gustave Aimard's earlier-published novel Les Francs-Tireurs (1861):
there is something more powerful than the brute force of bayonets: it is the idea whose time has come and hour struck
Original French: Il y a quelque chose de plus puissant que la force brutale des baïonnettes: c'est l'idée dont le temps est venu et l'heure est sonnée
Source: [The Freebooters, Gustave, Aimard, (tr. unknown), 1861, London, Ward and Lock, 57, http://hdl.handle.net/2027/chi.087603619?urlappend=%3Bseq=67]
Source: [Les Francs Tireurs, Gustave, Aimard, 1861, Paris, Amyot, 68, http://hdl.handle.net/2027/uc1.$b596684?urlappend=%3Bseq=76]
