The raid on Russell in 1845 led to the Northern War of 1845-1846. This would bring the British army to New Zealand in force, as Imperial troops garrisoned in New South Wales crossed the Tasman to join the war in Northland.
The British forces first engaged Hone Heke at his pa near Lake Omapere in May 1845. They landed at Oniwhero Bay and had an arduous march inland. The British lacked artillery and could only fire rockets that were more entertaining to Maori than effective. The results were inconclusive but both sides gained respect for one another.
In June the Ngati Hine war chief Te Ruki Kawiti, who had supported Heke, built a pa at Ohaeawai. He reasoned that it would divert the British from attacking his people in undefended villages.
Kawiti expected artillery so prepared for it. The pa had cleverly designed bunkers with firing positions at ground level. The palisades were covered with flax to shield the holes in the wall so the British couldn't see if there was a big enough breach to risk an assault.
On 1 July, the British commander, Colonel Henry Despard, ordered his men to charge the pa. The Maori defenders were behind palisades with one or two trenches in front so the troops coming at them had no chance. The Maori were outnumbered six to one but beat the army of the world's greatest empire.
Six months of uneasy truce ensued. Governor FitzRoy came under pressure from settlers to act decisively. He offered Kawiti and Heke a peace deal which included the confiscation of their land. Not surprisingly, they refused.
The final battle of the war was at Ruapekapeka pa in January 1846. Ruapekapeka, "the bat's nest", was described as a masterpiece of military construction. Here underground defenses could withstand shelling for many days.
On 11 January 1846 the British attacked the pa but found it empty except for the dead and wounded. The Maori defenders had gone into the bush behind hoping to draw the British into a trap. Some troops were killed but others continued to hold the pa. This allowed the new Governor, George Grey, to proclaim himself the victor of Ruapekapeka.
The Northern War eventually petered out. Governor Grey turned his attentions elsewhere as fighting erupted near Wellington where land disputes had escalated into full scale conflicts.