How does the shadow of the Middle-Earth War trigger the Lord of Light mission?

The Shadow Lord of Light in the Middle-earth War requires four siege missions to trigger.

Middle-earth: The Shadow of War continues the previous work, in which the ranger Talion entered into a contract with the necromancer Celebrimbor. In the flame of Mount Doom, the only thing that can challenge the Dark Lord was born: a new supreme ring. However, with the casting of the ring of power, the energy shock broke their vows, Celebrimbor was taken away, and Tarion, who was dying, put on the ring and embarked on a journey to find the necromancer.

After a long journey, Talion found the imprisoned Celebrimbor. It turned out that he was taken away by the body, and the body asked Talion to exchange the ring for the life of the necromancer. Talion agreed to her terms and became one again, challenging the zombie Luo wearing a ring, but was suppressed by her strength. After the corpse Luo revealed to him that Minas Ishir was besieged and the treasure Pallante would be taken away, Tarion and others began to rush to Minas Ishir to defend the last fortress of Gondor in Mordor and prevent Soren from obtaining Pallante.

The game plot has officially started.