George Tupou was established as the Tuʻi Haʻapai (H. king) before the death of his father in 1820.
He inherited the conflicts with the overlords of Tongatapu, in particular with Laufilitonga, the last Tuʻi Tonga, who tried to extend his role as spiritual leader into a more political one and contested Tāufaʻāhau in Haʻapai.
The culmination of this struggle was the Battle of Velata in 1826, in which Laufilitonga was defeated.
An important ally at that battle was the chief of Haʻafeva.

It was now clear that Tāufaʻāhau was very ambitious and wanted more than only Haʻapai.
To stop him, in 1827, the chiefs of Tongatapu made Laufilitonga the Tuʻi Tonga, and made Tāufa's uncle Aleamotuʻa a Tuʻi Kanokupolu, preventing an island invasion, as fighting against family members was seen as a Tongan disgrace.
In spite of this, at his baptism in 1831, Tāufa declared himself King George of Tonga.

His next conquest resulted from his relationships with Fīnau ʻUlukālala III, the ruler of Vavaʻu.
He became the Tuʻi Vavaʻu after Finau's death in 1833.
He dedicated Tonga (that is, Pouono in Vavaʻu) to God in 1839, assuring support from the missionaries.

During the 1830s, he resided in Vavaʻu, in Veitatalo, which is now ʻUlukālala's residence.
Vavaʻu was at peace and it prospered.
Tongatapu, on the other hand, suffered from a cruel civil war with the local chiefs fighting each other.
Tāufaʻāhau launched raids on Tongatapu with his fierce warriors from Haʻapai and Vavaʻu, the Tautahi (sea warriors).
 However, it was not until Aleamotuʻa's death that year, that he had an excuse to conquer Tongatapu.
The chiefs were forced to obey him, and he was installed as Tuʻi Kanokupolu in Kolovai on 4 December.
Niuafoʻou and Niuatoputapu would follow later. '
Eua was never  conquered by Tāufaʻāhau.
However, It was Kauvakauta of 'Eua whom conquered The Mighty  Kolo Tau o Velata in Ha'apai and assisted Tāufaʻāhau with guns and ammunition for his wars throughout Tonga.

In 1852, the last independent chief, Takai Mo Fa'e, fell and Tāufa became the undisputed leader of the whole of Tonga.
His rule saw many changes in Tongan politics.
He abolished serfdom in Vavaʻu in 1835, and published the Vavaʻu Code in 1838, the first written laws in Tonga.
However, he would not officially abolished serfdom everywhere in Tonga.
He opened the first parliament until 4 June 1862, which is still a public holiday called Emancipation Day, in Tonga.

He made Pangai Ha'apai the first capital of his realm in 1845.
 He then moved the capital to Nukuʻalofa in 1851 (resided in Lifuka from 1845 to 1851).
On 4 November 1875 (also a holiday), the constitution was promulgated and Tonga officially became a kingdom.
Siaosi then took the name George Tupou I, King of Tonga.
For this reason, both 1845 and 1875 are quoted as the beginning of his reign.
George Tupou was established as the Tuʻi Haʻapai (H. king) before the death of his father in 1820. He inherited the conflicts with the overlords of Tongatapu, in particular with Laufilitonga, the last Tuʻi Tonga, who tried to extend his role as spiritual leader into a more political one and contested Tāufaʻāhau in Haʻapai. The culmination of this struggle was the Battle of Velata in 1826, in which Laufilitonga was defeated. An important ally at that battle was the chief of Haʻafeva.
It was now clear that Tāufaʻāhau was very ambitious and wanted more than only Haʻapai. To stop him, in 1827, the chiefs of Tongatapu made Laufilitonga the Tuʻi Tonga, and made Tāufa's uncle Aleamotuʻa a Tuʻi Kanokupolu, preventing an island invasion, as fighting against family members was seen as a Tongan disgrace. In spite of this, at his baptism in 1831, Tāufa declared himself King George of Tonga.
His next conquest resulted from his relationships with Fīnau ʻUlukālala III, the ruler of Vavaʻu. He became the Tuʻi Vavaʻu after Finau's death in 1833. He dedicated Tonga (that is, Pouono in Vavaʻu) to God in 1839, assuring support from the missionaries.
During the 1830s, he resided in Vavaʻu, in Veitatalo, which is now ʻUlukālala's residence. Vavaʻu was at peace and it prospered. Tongatapu, on the other hand, suffered from a cruel civil war with the local chiefs fighting each other. Tāufaʻāhau launched raids on Tongatapu with his fierce warriors from Haʻapai and Vavaʻu, the Tautahi (sea warriors).  However, it was not until Aleamotuʻa's death that year, that he had an excuse to conquer Tongatapu. The chiefs were forced to obey him, and he was installed as Tuʻi Kanokupolu in Kolovai on 4 December. Niuafoʻou and Niuatoputapu would follow later. 'Eua was never  conquered by Tāufaʻāhau. However, It was Kauvakauta of 'Eua whom conquered The Mighty  Kolo Tau o Velata in Ha'apai and assisted Tāufaʻāhau with guns and ammunition for his wars throughout Tonga.
In 1852, the last independent chief, Takai Mo Fa'e, fell and Tāufa became the undisputed leader of the whole of Tonga. His rule saw many changes in Tongan politics. He abolished serfdom in Vavaʻu in 1835, and published the Vavaʻu Code in 1838, the first written laws in Tonga. However, he would not officially abolished serfdom everywhere in Tonga. He opened the first parliament until 4 June 1862, which is still a public holiday called Emancipation Day, in Tonga.
He made Pangai Ha'apai the first capital of his realm in 1845.  He then moved the capital to Nukuʻalofa in 1851 (resided in Lifuka from 1845 to 1851). On 4 November 1875 (also a holiday), the constitution was promulgated and Tonga officially became a kingdom. Siaosi then took the name George Tupou I, King of Tonga. For this reason, both 1845 and 1875 are quoted as the beginning of his reign.
George Tupou I