The Invasion of the Waikato became the largest and most important campaign of the 19th-century New Zealand Wars. Hostilities took place in the North Island of New Zealand between the military forces of the colonial government and a federation of Mori tribes known as the Kingitanga Movement. The Waikato is a territorial region with a northern boundary somewhat south of the present-day city of Auckland. The campaign lasted for nine months, from July 1863 to April 1864. The invasion was aimed at crushing Kingite power (which European settlers saw as a threat to colonial authority) and also at driving Waikato Mori from their territory in readiness for occupation and settlement by European colonists. The campaign was fought by a peak of about 14,000 Imperial and colonial troops and about 4,000 Mori warriors drawn from more than half the major North Island tribal groups.Plans for the invasion were drawn up at the close of the First Taranaki War in 1861 but the Colonial Office and New Zealand General Assembly opposed action, and the incoming Governor Sir George Grey (second term 18611868) suspended execution in December of that year. Grey reactivated the invasion plans in June 1863 amid mounting tension between Kingites and the colonial government and fears of a violent raid on Auckland by Kingite Mori. Grey used as the trigger for the invasion Kingite rejection of his ultimatum on 9 July 1863 that all Mori living between Auckland and the Waikato take an oath of allegiance to Queen Victoria or be expelled south of the Waikato River. Government troops crossed into Waikato territory three days later and launched their first attack on 17 July at Koheroa, but were unable to advance for another 14 weeks.

The subsequent war included the Battle of Rangiriri (November 1863)which cost both sides more men than any other engagement of the New Zealand Warsand the three-day-long Battle of rkau (MarchApril 1864), which became arguably the best-known engagement of the New Zealand Wars and which inspired two films called Rewi's Last Stand. The campaign ended with the retreat of the Kingitanga Mori into the rugged interior of the North Island and the colonial government confiscating about 12,000 km2 of Mori land.

The defeat and confiscations left the King Movement tribes with a legacy of poverty and bitterness that was partly assuaged in 1995 when the government conceded that the 1863 invasion and confiscation was wrongful and apologised for its actions. The WaikatoTainui tribe accepted compensation in the form of cash and some government-controlled lands totalling about $171 millionabout 1 percent of the value of the lands confiscated in 1863and later that year Queen Elizabeth II personally signed the Waikato Raupatu Claims Settlement Act 1995.

(The Governor-General normally gives Royal Assent to legislation by signing on the monarch's behalf.)

The New Zealand Wars took place from 1845 to 1872 between the New Zealand Colonial government and allied Māori on one side and Māori and Māori-allied settlers on the other. They were previously commonly referred to as the Land Wars or the Māori Wars, while Māori language names for the conflicts included Ngā pakanga o Aotearoa ("the great New Zealand wars") and Te riri Pākehā ("the white man's anger"). Historian James Belich popularised the name "New Zealand Wars" in the 1980s, although the term was first used by historian James Cowan in the 1920s.Though the wars were initially localised conflicts triggered by tensions over disputed land purchases, they escalated dramatically from 1860 as the government became convinced it was facing united Māori resistance to further land sales and a refusal to acknowledge Crown sovereignty. The colonial government summoned thousands of British troops to mount major campaigns to overpower the Kīngitanga (Māori King) movement and also acquire farming and residential land for British settlers. Later campaigns were aimed at quashing the so-called Hauhau movement, an extremist part of the Pai Mārire religion, which was strongly opposed to the alienation of Māori land and eager to strengthen Māori identity.At the peak of hostilities in the 1860s, 18,000 British Army troops, supported by artillery, cavalry and local militia, battled about 4,000 Māori warriors in what became a gross imbalance of manpower and weaponry. Although outnumbered, the Māori were able to withstand their enemy with techniques that included anti-artillery bunkers and the use of carefully placed pā, or fortified villages, that allowed them to block their enemy's advance and often inflict heavy losses, yet quickly abandon their positions without significant loss. Guerrilla-style tactics were used by both sides in later campaigns, often fought in dense bush. Over the course of the Taranaki and Waikato campaigns, the lives of about 1,800 Māori and 800 Europeans were lost, and total Māori losses over the course of all the wars may have exceeded 2,100.

Violence over land ownership broke out first in the Wairau Valley in the South Island in June 1843, but rising tensions in Taranaki eventually led to the involvement of British military forces at Waitara in March 1860. The war between the government and Kīngitanga Māori spread to other areas of the North Island, with the biggest single campaign being the invasion of the Waikato in 1863–1864, before hostilities concluded with the pursuits of Riwha Tītokowaru in Taranaki (1868–1869) and Rangatira (chief) Te Kooti Arikirangi Te Turuki on the east coast (1868–1872).

Although Māori were initially fought by British Army forces, the New Zealand government developed its own military force, including local militia, rifle volunteer groups, the specialist Forest Rangers and kūpapa (pro-government Māori). The government also responded with legislation to imprison Māori opponents and confiscate expansive areas of the North Island for sale to settlers, with the funds used to cover war expenses; punitive measures that on the east and west coasts provoked an intensification of Māori resistance and aggression.