"In the growth of the civilization and the development of the nations, the trend toward disappearance of the gaps between the two sexes started." I'd change it like this because your previous structure implied that somebody in particular grew the civilization and developed the nations, which isn't really true. Also, I didn't change this because I can't be sure without context that it's incorrect, but unless you're talking about a specific civilization, you can leave out the "the." And, while correct, this version still seems a little unnecessarily wordy. Here is what I would say: "In the growth of the civilization and the development of the nations, the gaps between the two sexes started to disappear."

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