Rashi to Genesis 11:9

ומשם הפיצם: למד שאין להם חלק לעולם הבא. וכי אי זו קשה, של דור המבול או של דור הפלגה, אלו לא פשטו יד בעיקר, ואלו פשטו יד בעיקר כביכול להלחם בו, ואלו נשטפו, ואלו לא נאבדו מן העולם. אלא שדור המבול היו גזלנים והיתה מריבה ביניהם לכך נאבדו, ואלו היו נוהגים אהבה וריעות ביניהם, שנאמר שפה אחת ודברים אחדים. למדת ששנוי המחלוקת וגדול השלום

And from thence (did the Lord) scatter them This teaches that they have no portion in the world to come. But which (transgression) was more grave, that of the generation of the Flood or that of the generation of the division (of mankind)? The former did not stretch forth their hands against G-d, while the latter did stretch forth their hands against the Almighty to wage war against him; yet the former were drowned while the latter did not perish from the world. However, the generation of the Flood were robbers and there was strife among them, therefore they were destroyed; whereas the latter used to conduct themselves with love and friendship among them, for it is stated "of one language and of one speech." (From the above) you learn that hated is dissension and great is peace.