AP Photo

This weekend, in Juba, South Sudan, Africa’s 54th nation was born. Millions of people are celebrating a new national identity and new national promise. Like on our own July Independence Day 235 years ago, there is reason to hope for a better future — if the people and leaders of both Sudan and South Sudan commit themselves to the hard work ahead.

This day was far from inevitable. For more than two decades, Sudan has been riven by intense fighting over land and resources. Just a year ago, talks between the...