The Agri Decumates was lost to the Romans in c.262, regained by Aurelian and Probus in 275–8, and lost again sometime between 290 and 310. The losses here seem not so much due to any rise in power of the local Alemanni tribe, but Roman internal division. When rival Roman factions controlled Gaul and Raetia, as was the case in 262–274 and 306, the limes of the Agri Decumates were no longer defensible and had to be abandoned.
In late 284, during the war between Carinus and Diocletian, peasants and brigands in northern Gaul joined in revolt under the leadership of Amandus and Aelianus. These rebels soon became known as the Bagaudae—possibly from the Gaulish word for “warrior”—and swiftly grew in numbers, threatening many cities across the countryside. To deal with the situation, Diocletian appointed his faithful general Maximian as Caesar in July 285. Maximian quickly marched to Gaul and by early 286 had suppressed the uprising.in wikipedia
During the Crisis of the Third Century, the Baquates and other Berber tribes became increasingly aggressive, forcing more and more concessions from the Roman inhabitants of southern Mauretania Tingitana. This came to an end in around 284–285, when, for unknown reasons, Roman authorities evacuated Volubilis and other cities south of the Loukkos river to fall back on Tingis (Tangier). Although the region would never be retaken by the Romans, Diocletian eventually secured land communications between Mauretania Tingitana and Mauretania Caesariensis by forming an alliance with the Baquates.in wikipedia
In July 285 the Roman emperor Carinus advanced to meet the usurper Diocletian near Margum, on the Margus river, in Upper Moesia. Despite having superior numbers and apparently coming close to winning the battle, the emperor was abandoned by his own troops and defeated. Carinus died soon afterwards, possibly murdered by one of his own officers when he took refuge in the Danube fort of Cornacum (Sotin, Croatia), leaving Diocletian as sole ruler of the Roman Empire.in wikipedia