The Orange Free State (Dutch: Oranje Vrijstaat; Afrikaans: Oranje-Vrystaat;) was an independent Boer sovereign republic under British suzerainty in Southern Africa during the second half of the 19th century, which ceased to exist after it was defeated and surrendered to the British Empire at the end of the Second Boer War in 1902. It is one of the three historical precursors to the present-day Free State province.Extending between the Orange and Vaal rivers, its borders were determined by the United Kingdom of Great Britain and Ireland in 1848 when the region was proclaimed as the Orange River Sovereignty, with a British Resident based in Bloemfontein. Bloemfontein and the southern parts of the Sovereignty had previously been settled by Griqua and by Trekboere from the Cape Colony.

The Voortrekker Republic of Natalia, founded in 1837, administered the northern part of the territory through a landdrost based at Winburg. This northern area was later in federation with the Republic of Potchefstroom which eventually formed part of the South African Republic (Transvaal).Following the granting of sovereignty to the Transvaal Republic, the British sought to drop their defensive and administrative responsibilities between the Orange and Vaal rivers, while local European residents wanted the British to remain. This led to the British recognising the independence of the Orange River Sovereignty and the country officially became independent as the Orange Free State on 23 February 1854, with the signing of the Orange River Convention. The new republic incorporated the Orange River Sovereignty and continued the traditions of the Winburg-Potchefstroom Republic.The Orange Free State developed into a politically and economically successful republic and for the most part enjoyed good relationships with its neighbours. It was annexed as the Orange River Colony in 1900. It ceased to exist as an independent Boer republic on 31 May 1902 with the signing of the Treaty of Vereeniging at the conclusion of the Second Boer War. Following a period of direct rule by the British, it attained self-government in 1907 and joined the Union of South Africa in 1910 as the Orange Free State Province, along with the Cape Province, Natal, and the Transvaal. In 1961, the Union of South Africa became the Republic of South Africa.The Republic's name derives partly from the Orange River, which in turn was named in honour of the Dutch ruling family, the House of Orange, by the Dutch explorer Robert Jacob Gordon. The official language in the Orange Free State was Dutch.

The Second Boer War (Afrikaans: Tweede Vryheidsoorlog, lit. "Second Freedom War", 11 October 1899 – 31 May 1902), also known as the Boer War, the Anglo–Boer War, or the South African War, was a conflict fought between the British Empire and the two Boer Republics (the South African Republic and the Orange Free State) over the Empire's influence in Southern Africa from 1899 to 1902. Triggered by the discovery of diamond and gold deposits in the Boer republics, the Boers launched successful attacks against British outposts in the opening stages of the war before being pushed back by imperial reinforcements. Though the British swiftly occupied the Boer republics, numerous Boers refused to accept defeat and engaged in guerrilla warfare. Eventually, British scorched earth policies brought the remaining Boer guerillas to the negotiating table, ending the war.The conflict broke out in 1899 after the failure of the Bloemfontein Conference and Boer irregulars and militia attacked colonial settlements in nearby British colonies. Starting in October 1899, the Boers placed Ladysmith, Kimberley, and Mafeking under siege, and won a string of victories at Colenso, Magersfontein and Stormberg. In response to these developments, increased numbers of British Army soldiers were brought to Southern Africa, and mounted largely unsuccessful attacks against the Boers. However, British military fortunes changed when their commanding officer, General Redvers Buller was replaced by Lord Roberts and Lord Kitchener, who relieved the three besieged cities and invaded the two Boer Republics in early 1900 at the head of a 180,000-strong expeditionary force. The Boers, aware they were unable to resist such a large force, chose to refrain from fighting pitched battles, allowing the British to occupy both republics and their capitals, Pretoria and Bloemfontein.Boer politicians, including President of the South African Republic Paul Kruger either fled the region or went into hiding; the British Empire officially annexed the two republics in 1900. In Britain, the Conservative ministry led by Lord Salisbury attempted to capitalise on British military successes by calling an early general election, which was dubbed by contemporary observers as a "khaki election". However, numerous Boer fighters took to the hills and launched a guerrilla campaign against the British occupational forces, becoming known as bittereinders. Led by prominent generals such as Louis Botha, Jan Smuts, Christiaan de Wet, and Koos de la Rey, Boer guerrillas launched a campaign of hit-and-run attacks and ambushes against the British, which would continue for two years.The Boer guerrilla campaign proved difficult for the British to defeat, due in part to British unfamiliarity with guerrilla tactics and extensive support for the guerrillas among the civilian population in the Boer Republics. In response to continued failures to defeat the Boer guerillas, British high command ordered several scorched earth policies to be implemented as part of a large scale and multi-pronged counterinsurgency campaign; a complex network of nets, blockhouses, strongpoints and barbed wire fences was constructed, virtually partitioning the occupied republics. British troops were ordered to destroy farms and slaughter livestock to deny them to Boer guerillas, and over a hundred thousand Boer civilians (mostly women and children) were forcibly relocated into concentration camps, where 26,000 died of various causes, mostly starvation and disease. Black Africans in the same areas were also interned in concentration camps as well to prevent them from supplying the Boers; 20,000 died in the camps as well, largely due to the same causes as their Boer counterparts.In addition to these scorched earth policies, British mounted infantry units were deployed to track down and engage individual Boer guerillas units; by this stage of the war, all battles being fought were small-scale skirmishes. Few combatants on either side were killed in action, with most casualties coming via disease. Lord Kitchener began to offer generous terms of surrender to remaining Boer leaders in an effort to bring an end to the conflict. Eager to ensure their fellow Boers were released from the concentration camps, the majority of Boer commanders accepted the British terms in the Treaty of Vereeniging, formally surrendering in May 1902. The former republics were transformed into the British colonies of the Transvaal and Orange River, and in 1910 were merged with the Natal and Cape Colonies to form the Union of South Africa, a self-governing dominion within the British Empire.British expeditionary efforts were aided significantly by local colonial forces from the Cape Colony, the Natal Colony, Rhodesia, as well as volunteers from the British Isles and the British Empire worldwide, particularly Australia, Canada, India and New Zealand. Later in the war, Black African recruits contributed increasingly to the British war effort. International public opinion was generally sympathetic to the Boers and hostile to the British. Even within the United Kingdom, there existed significant opposition to the war. As a result, the Boer cause attracted thousands of volunteers from neutral countries all over the world, including German Empire, United States, Russia and even some parts of the British Empire such as Australia and Ireland. Many consider the Boer War as marking the beginning of the questioning of the British Empire's veneer of impenetrable global dominance; this is due to the war's surprisingly long duration and the unforeseen, discouraging losses suffered by the British fighting the "cobbled-together army" of Boers.