Born in Carnot, Ubangi-Shari,[note 1] Banza served with the French Army during the First Indochina War before joining the Central African Armed Forces.
As commander of the Camp Kassaï military base in 1965, Banza helped Jean-Bédel Bokassa overthrow the government of President David Dacko.
Recognizing Bokassa's attempts to undermine him, Banza made a number of remarks highly critical of the president's handling of the government.
[4] In his twenties, he had served with the French army in the First Indochina War and had been stationed in Gabon, Morocco, Tunisia and other locations in colonial Africa.
[6] He had a similar military record to his future colleague Jean-Bédel Bokassa, who had also served in the First Indochina War and had been stationed in Africa and Europe as a radio transmissions expert.
Brian Titley, author of Dark Age: The Political Odyssey of Emperor Bokassa described Banza as an "intelligent, ambitious, and unscrupulous" military officer.
[6] Central African Republic President David Dacko, Bokassa's cousin, took over the country in 1960,[2] after winning a power struggle against Abel Goumba.
[6] After receiving word of the coup from the country's military chief of staff, Albert-Bernard Bongo, officials in Paris sent paratroopers to Gabon and restored M'ba to power in a matter of hours.
[12] Banza, who was then commander of the Camp Kassaï military base in northeast Bangui, offered Bokassa his support and persuaded the still-worried commander-in-chief to carry out the coup.
Early in the evening of 31 December 1965, Dacko left the Palais de la Renaissance to visit one of his minister's plantations southwest of the capital.
[6] At 22:30 WAT (UTC 21:30), Captain Banza gave orders to his officers to begin the coup; one of his subordinates was to subdue the security guard in the presidential palace, while the other was to take control of Radio-Bangui to prevent communication between Dacko and his followers.
[13] Bokassa called Izamo at his headquarters, asking him to come to Camp de Roux to sign some papers that needed his immediate attention.
Bokassa began to panic, as he believed the president had been warned of the coup in advance, and immediately ordered his soldiers to search for Dacko in the countryside until he was found.
After leaving his minister's plantation near midnight, he headed to Simon Samba's house to ask the Aka Pgymy leader to conduct a year-end ritual.
After Bokassa reciprocated by meeting Tombalbaye on 2 April 1966 along the southern border of Chad at Fort Archambault, the two decided to help one another if either was in danger of losing power.
[16] After Bokassa threatened to withdraw from the franc monetary zone, French President Charles de Gaulle decided to make an official visit to the Central African Republic on 17 November 1966.
Bokassa moved to Camp de Roux, where he felt he could safely run the government without having to worry about Banza's thirst for power.
Bokassa recognized what his minister was doing, so he sent military units most sympathetic to Banza to the country's border and brought his own army supporters as close to the capital as possible.
[20] A year later, after Banza made a number of remarks highly critical of Bokassa and his management of the economy, the president, perceiving an immediate threat to his power, removed him as his minister of state.
[20] Banza revealed his intention to stage a coup to Lieutenant Jean-Claude Mandaba, the commanding officer of Camp Kassaï, who he looked to for support.
Banza's mistress, Julienne Kombo, who entered the Palais de la Renaissance crying hysterically after her lover's death, was arrested and jailed until 24 June 1972.
Gbaguili served as a witness in Bokassa's criminal trials for treason, murder, cannibalism and embezzlement during the 1980s, explaining in detail the numerous crimes and human rights violations the former dictator had completed.
According to Brian Titley, author of Dark Age: The Political Odyssey of Emperor Bokassa, he surrounded himself with "sycophants, who were all too willing to nurture his growing delusions of grandeur"; with no one to stop him, he also spent money with reckless abandon.