ðɪs θˈiəɹi mˈɛnt ðæt ɪf ðɪ ˈiːst stˈɑːɹɾᵻd fˈɪlɪŋ ˌʌp wɪð ˈɪmɪɡɹənts, ðeɪ kʊd ˈɔːlweɪz ɡˌoʊ wˈɛst ʌntˈɪl ðeɪ ɹˈiːtʃt ɐ pˈɔɪnt wˌɛɹ ðeɪ kʊd nˌɑːt mˈuːv ˌɛni fˈɑːɹðɚ.
This theory meant that if the East started filling up with immigrants, they could always go West until they reached a point where they could not move any farther.