In order to equalize the number of teams in each conference, three NFL teams that predated the AFL's launch (the Cleveland Browns, Pittsburgh Steelers, and the then-Baltimore Colts) joined the ten former AFL teams to form the AFC.
ɪn ˈɔːɹdɚ tʊ ˈiːkwəlˌaɪz ðə nˈʌmbɚɹ ʌv tˈiːmz ɪn ˈiːtʃ kˈɑːnfɹəns, θɹˈiː ˌɛnˌɛfˈɛl tˈiːmz ðæt pɹɪdˈeɪɾᵻd ðɪ ˌeɪˌɛfˈɛlz lˈɑːntʃ ðə klˈiːvlənd bɹˈaʊnz, pˈɪtsbɜːɡ stˈiːlɚz, ænd ðə ðˈɛnbˈɔltɪmˌoːɹ kˈoʊlts dʒˈɔɪnd ðə tˈɛn fˈɔːɹmɚɹ ˌeɪˌɛfˈɛl tˈiːmz tə fˈɔːɹm ðɪ ˌeɪˌɛfsˈiː.