Although the United Kingdom of Portugal ceased to exist de facto beginning in , he remained its monarch de jure between and After the recognition of the independence of Brazil under the Treaty of Rio de Janeiro of , he continued as King of Portugal until his death in Under the same treaty, he also became titular Emperor of Brazil for life, while his son, Emperor Pedro I , was both de facto and de jure the monarch of the newly independent country.
From , he served as prince regent due to the mental illness of his mother. In , he succeeded his mother as monarch of the Portuguese Empire , with no real change in his authority, since he already possessed absolute powers as regent. One of the last representatives of absolute monarchy in Europe, John VI lived during a turbulent period; his reign never saw a lasting peace. Throughout his period of rule, major powers, such as Spain , France.
Forced to flee across the Atlantic Ocean to Brazil when troops of the Emperor Napoleon I invaded Portugal, he found himself faced there with liberal revolts; he was compelled to return to Europe amid new conflicts.
His marriage was no less conflictual, as his wife Carlota Joaquina of Spain repeatedly conspired against her husband in favor of personal interests or those of her native Spain. John lost Brazil when his son Pedro declared independence, and his other son Miguel later Miguel I of Portugal led a rebellion that sought to depose him. According to recent scholarly research, his death may well have been caused by arsenic poisoning. Notwithstanding these tribulations John left a lasting mark, especially in Brazil, where he helped to create numerous institutions and services that laid a foundation for national autonomy, and many historians consider him to be a true mastermind of the modern Brazilian state.
John's contemporaries viewed him as a kind and benevolent king, although later generations of Portuguese and Brazilians have made him the subject of frequent caricature.
