Lojban was started in 1987 by a group of Loglanists (who now call themselves The Logical Language Group) who disagreed with some of The Loglan Institute's policies. Since the disagreements were not linguistic in nature, Lojban started out conceptually very similar to Loglan, although it has a different vocabulary in order to avoid copyright issues. Since the groups have not interacted much since, there has been some "linguistic drift".
By the way, the two groups use the word "Loglan" in different ways. The Loglan Institute (the original group) calls only their language "Loglan", while The Logical Language Group (the Lojban people) calls the class that both languages belong to "Loglan".