The Bands operated like an independent force from the larger part of the army of the League (led by Francesco Maria della Rovere, duce of Urbino). The “Gran Diavolo” (the Big Devil, which Giovanni was called) with his chavalry and archibusers was a torment for the imperials directed to Rome, creating many difficulties for them. His death revealed the duce of Urbino's lack of military virtues when he left the road free to the enemy.
The Bande Nere survived the death of Giovanni for two years.
The beginning of 1527 again proved their efficency when they defended Frosinone from the army of the Vicere' of Naples. In April of the same year, Clemente VII, hoping to lighten himself of onerous expenses that the maintenance of mercenary troops involved, took advantage of his agreement with Carlo di Lannoy and betrayed by Carlo di Borbone. This shot was fired “very imprudently” according to the Guicciardini writes. A thousand Bande Nere were collected from Renzo da Ceri after that the pope had finally realized that the imperials would have invaded Rome. They tried to defend the city from the enemy onslaught and most were killed on the walls.

The Bands would next be employed by Florence and were entrusted to Orazio Baglioni. Under him they participated in the foolish expedition led by Odet de Foix, Visconte of Lautrec, for the conquest of the reign of Naples. During this campaign they had more opportunity to demonstrate their value. They were prone, however, to demonstrations of cruelty and ferocity, such as in the invasion of Melfi “where,” so writes the Sannuto, “they rushed in, killing anyone on their path, soldiers, men and women, and the children too, taken prisoners, and sacked and plundered the land. No one saved himself, except those who jumped down the walls, killing themselves or being taken or killed.”
Orazio Baglioni fell in battle in Naples on 22 May 1528.
At the end of August the Bands, stricken with continuous struggle and plague, surrendered to he imperials together along with the rest of the League army, ending their existence.

The name of "Black" with which the bands of Giovanni de' Medici passed to the history, and with which same they began to call themselves after the death of their leader, was due to the color of their flags that Giovanni had changed from white and viol to black in sign of mourning for the death of the uncle, Pope Leone X.

The Black Bands represented the best expression of the "Italian" strategy and tactics emerged in the course of the renaissance wars. Composing largely of archibusers, they utilized very fast light troops, specialized in the “little war”. While in the big campaign struggle they weren't able to sustain the clash of big massed pikeman squares if not supported themselves by framed infantry in a closed order, they were the best “the market” could offer in the guerrilla, close combat, vanguard and cover operations. So, the struggling factions contended for their services, each side increasing their offer in an attempt to outbid the other.

Nevertheless Giovanni was a professionist of war and also a much skillful one, and so he was really well payed for his service. However it wasn't only money to attract him, but also the hope that, forming an alliance once with someone and then with someone else, he could get his own feud. The money, and it was really a big amount, was indispensable for paying the soldiers and so keep united the company of his Bands. In an age where all was for sale, he remained however faithful to Florence andto the Medici family, reppresented in that period by the popes Leone X and Clemente VII.
Until the first was alive, Giovanni remained sided with the hispanish-imperials, allied with the Church.
With Leone X death, he passed to the french, then again to the spanish side and then, enticed by the rich proposal of Francesco I, got back with the french (and the new pope, Clement VII, gave his preference to the King of France). From that moment, he became the implacable enemy of the german landsknechts that gratified him with the significant nickname of Big Devil (“Gran Diavolo”).

The popularity of Giovanni and his Bands did spread very fast. Joined them, like witnesses again the Guicciardini, the “best Italian soldiers that took payment”; many joined for adventure spirit more than from true thirst of income, since discipline was much more severe than in other formations and the payment usually was slow to come and sometimes it didn't come at all. In their rows there were failed men of literature, sons of broken noble families or seeking a little honour, adventurer professionisti, desperates and refused of society, farmers who for avoiding to starve to death joined to do someone else what was done to them. Skillful with archebus and sword, these soldiers mutated from Big Devils on the battlefield to devils of the robbery, violence and plunder when there was the occasion and expecially when the payment was very slow to come. Between them there were also deserter and traitors. The firsts, once taken, were hung, while the latter, until found, were inexorably “passed to the pikes” from their companions, to simbolise the collective punishment that struck who didn't respect the oath to the captain and to the loyal tie to his companions.
The Black Bands haven't ever been much numerous. Even in their best period, has never been more than 4000 units. At Caprino against Swiss there were 200 units of heavy chavalrly, 300 light and 3000 archibusers; in Pavia 50 units of heavy chavalry, 200 light and about 2000 infantry. In Governolo Giovanni attacked the imperials with 400 archibusers, that was bringed on the battlefield by as many knights. Frosinone was defended by 1800 infantry.
The Bands was composed quite all by italians, most from Tuscany and Romagna, probably with others from Lombardia during the period where Giovanni operated in the nothern part of Italy. Men from the appennino between Tuscany and Emilia was cheap and, at least at the beginning of their military career, with little pretends; moreover foreign mercenaries, far from home, were less trusted and more inclined to disertion and to change their master.
In the passage of short time, under the guide of Giovanni, the Bands became an elite formation, with little replies in the panorama of the Italian companies of fortune, of which they constituted the last and most important example. They had short life, like their young condottiero. With him they entered in history, after his death they became legend.