"Deep anger" refers to a strong and intense feeling of resentment or fury that is deeply rooted and may last for a prolonged period of time. Full definition
This has been the underlying issue of the election campaign: That there is a very real very deep anger that politicians do not represent the wishes of the people that have elected them. (politics.co.uk)
Participants, who have often experienced deep anger towards themselves or others, experience forgiveness. (faith.org.uk)
The Boko Haram insurgency is a (source of) deep anger of the Kanuri against the Fulani that has merged into the pre-existing Boko Haram issue. (punchng.com)