Here, it is quite probable that lightning and celestial fires allude to bombings or any other manifestation coming from the sky. This suggests one of our 20th century wars: there were no air-battles before World War I.

Interpretation

Once again, a foreign army invades Italy
And bombs Naples, Palermo, Syracusa and all Sicily.

History

The allies enter Palermo

The new tyrants are the allies who, in the spring of 1943, were about to land in Sicily and Italy in order to throw out the Germans and occupy, in turn, the country.
During World War II, the four above mentioned towns were strategic points of defence of the german army, but they were also the sites chosen for the landing in Sicily and Italy in 1943, and this is why the allies bombed heavily these locations in order to ensure the safety of their troops during the landing.
4 Avril 1943:
Violent aerial raids [fulgures feux célestes] on Naples, Palermo et Syracusa (in Sicily) and Caloforte (in Sardinia): only for Naples, the official report gives 221 deaths and 387 wounded.
...April 17, 1943:
A new raid by american bombers [nouveaux tyrans] on Palermo, Catania and Syracusa causes great damage and many deaths.
...July 2, 1943:
The ports of central and southern Italy continue to be the target of aerial raids by the allies. [nouveaux tyrans] From June 12 to July 2, the anglo-american bombers have unloaded more than 2000 tons of bombs.
...July 14, 1943:
The bombing intensifies on communication routes that join up the north and south of the peninsula, and on the most important centres of the south: Naples is the preferred target..
[Translation - La Seconde Guerre Mondiale au Jour le Jour, Cesare Salmaggi et Alfredo Palavisini]