The Catholic Church strongly discourages the enforced practice of endogamy since it diminishes the freedom of individual(s) to marry their divinely intended spouse. When practiced, endogamy is usually based on ethnic, cultural or racial considerations rather than religious factors as was recently manifested in the controversial Knanaya Church in India (coincidentally, I am a classmate of Bishop Michael Mulhall who investigated this practice on behalf of the Vatican).
In short, people should be free to marry without geographical or tribal borders preventing them from it.
With that said, Catholics are encouraged to marry spouses who share the same or similar religious beliefs since shared faith means shared values, which can help them navigate difficult situations and decision in marriage and family life. Sharing a common faith also provides mutual encouragement and incorporates a spiritual dimension to their marriage that can become an opening of grace when they most need it.