Peter's rule was marked with the great exercise of political liberties, freedom of the press, national, economical and cultural rise, and it is sometimes dubbed a "golden" or "Periclean age".

During this period, he pursued interests such as photography and painting, and read works of political philosophy, learning about liberalism, parliamentarism and democracy.

[7] At the outbreak of the 1870–71 Franco-Prussian War, Peter joined the French Foreign Legion under the pseudonym Petar Kara, together with relative Nikola Nikolajević.

He adopted the nom de guerre of Petar Mrkonjić, and upon reaching the regions of Banija and Kordun in Austria-Hungary, took control of a guerrilla unit of about 200 men.

He discovered that Prince Milan of Serbia was plotting to assassinate him fearing that Peter would attempt to wrest back the throne from the Obrenović dynasty.

Prior to his departure, he wrote a letter to Milan explaining why he was leaving the battlefield and offering to make peace with the Obrenović dynasty.

He decided to travel to Kragujevac, the seat of the Royal Serbian Government, and address the National Assembly in an attempt to clear his name.

[10] During his exile, Peter proposed himself as a suitor to Princess Feodora of Saxe-Meiningen, niece of Wilhelm II, who was thirty-six years his junior, though this was likely a bid to gain support of the Kaiser for succeeding to the Serbian throne.

Following the Royal Serbian Army's rout in the Serbo-Bulgarian War of 1885, Peter and Nicholas devised a plan to invade Serbia and overthrow the Obrenović dynasty.

Due to his precarious financial situation, which prevented him from sending the boys to private schools in Switzerland, Peter accepted the Tsar's offer.

[13] In July 1900, King Alexander, Milan's 23-year-old son, married Draga Mašin, a widowed lady-in-waiting twelve years his senior with a reputation for promiscuity.

The officers, led by Dragutin Dimitrijević ("Apis"), initially sought to expel Alexander and Draga but realized that doing so would precipitate a conflict between the pro-Karađorđević and pro-Obrenović camps within the country.

[14] Political conditions in Europe were such that the proclamation of a republic would only have increased the ire of the Great Powers towards Serbia in case Alexander was overthrown, giving Austria-Hungary a pretext to invade.

[18] Russia immediately recognized the National Assembly's decision declaring Peter the next King of Serbia and expressed satisfaction that the inter-dynastic intrigues which had plagued the country since the early-19th century had been brought to an end.

[18] The year-long interval between Peter's return to Serbia and his coronation deliberately made the ceremony coincide with the 100th anniversary of the First Serbian Uprising with the hope of giving European statesmen time to come to terms with the palace coup.

[22] Arnold Muir Wilson, the honorary Serbian consul in Sheffield, and his cameraman, Frank Mottershaw, filmed King Peter's procession and a parade following the coronation.

Serbia, which had helped arm the Albanian Catholic and Hamidian rebels and had sent secret agents to some of the prominent leaders, took the revolt as a pretext for war.

[citation needed] The agreement provided that, in the event of victory against the Ottomans, Bulgaria would receive all of Macedonia south of the Kriva Palanka-Ohrid line.

Peter I led the Serbian army alongside marshals like Radomir Putnik, Stepa Stepanović, Božidar Janković and Petar Bojović.

Peter I became gradually very popular for his commitment to parliamentary democracy that, in spite of certain influence of military cliques in political life, functioned properly.

[citation needed] King Peter himself favored the idea of a broader coalition government that would boost Serbian democracy and help pursue an independent course in foreign policy.

In contrast to the Austrophile Obrenović dynasty, King Peter I relied on Russia and France, which provoked rising hostility from expansionist-minded Austria-Hungary.

King Peter I paid two solemn visits to Saint-Petersburg and Paris in 1910 and 1911 respectively, to be greeted as a hero both of democracy and of national independence in the troublesome Balkans.

[citation needed] The territory of Serbia doubled and her prestige among South Slavs (Croats and Slovenes in particular, and among the Serbs in Austria-Hungary, in Bosnia-Herzegovina, Vojvodina, the Military Frontier, Dalmatia, Slavonia, etc.)

After the conflict between military and civilian representatives in the spring of 1914, King Peter chose to "retire" due to ill health, reassigning on 11/24 June 1914 his royal prerogatives to his second son heir apparent Crown Prince Alexander.

[citation needed] The retired King, spending most of his time in various Serbian spas, remained relatively inactive during the First World War, although occasionally, when the military situation became critical, he visited trenches on the front-line to check up on morale of his troops.

Following the invasion of Serbia by the joint forces of Germany, Austro-Hungary and Bulgaria in October 1915, King Peter I led the army and tens of thousands of civilian refugees through the high mountains of Albania to the Adriatic sea on a "Calvary known to few peoples".

He was solemnly buried in his endowment in Oplenac, the Church of Saint George in the vicinity of Topola in Central Serbia, where his grandfather Karađorđe, the founder of the dynasty, had launched a large-scale insurrection against the Ottomans in 1804.

Three cities in interwar Yugoslavia were named after King Peter I: Mrkonjić Grad in Bosnia-Herzegovina (former Varcar Vakuf), Petrovgrad in Vojvodina (Veliki Bečkerek, now Zrenjanin) and Petrovac na Moru (former Kaštel Lastva) in Montenegro.

The other monuments in honor to King Peter I were restored or erected in Republika Srpska, in Bosnia and Herzegovina where his cult status as a national hero is as strong as it is in Serbia.