When Aurelian died in A.D. 275, the senate appointed Marcus Claudius Tacitus as emperor in his stead. Tacitus was already elderly at the time, which makes one wonder if he accepted the post because he was power-hungry, or merely senile. In A.D. 276, Tacitus was murdered by his own troops at Tyana. Perhaps he should have treated them better.
This left a power vacuum which was filled by the Marcus Annius Florianus (commonly known as Florian), who was the praetorian prefect of Tacitus. When Tacitus died, Florian seized control of the empire and was recognized as emperor everywhere except Syria and Egypt, which were under the control of Marcus Aurelius Probus. Probus demoralized Florian's troops to the point that they killed Florian.
So Probus outflanked Florian at Tarsus and became the sole emperor. Probus owed his position at emperor to the army, but he too had to deal with several rebellions by the army, such as those of Saturninus in the East (277-78), Proculus and Bonosus in Gaul (280), and a revolt in Britain. So the army was not exactly happy with Probus's rule. In 282, Probus was killed by his own troops, after some of his troops deserted to Carus, who was proclaimed emperor by army renegades.
Roman history of this time period begins to sound like the same thing over and over with only the names changing.