Although this war started because of president Laurent Désiré-Kabila's sudden break of ties with Rwanda, leading to a Rwandan invasion to end Tutsi persecution in Eastern Congo, it quickly became more complicated. Through the backing of various opposing rebel groups by the Kabila government and both Rwanda and Uganda, and the backing of the Kabila government by Angola, Zimbabwe, Namibia, Sudan, Chad and Libya, the situation quickly descended into that of a proxy war. Such a state of warfare, with so many sides and complex factors simply complicates and prolongs war, bringing warfare closer to attrition.
Taking lessons from this conflict should start with ending proxy warfare and making the financial support or supply of arms to a country in conflict, especially that of a civil war, heavily restricted by a unified multinational organisation such as the UN. Making proxy wars less easy to extend and profit from would go a long way to minimising such long standing, complex and bloody conflicts. This would benefit other countries with long standing complex conflicts, such as Israel/Palestine, and would at least help minimise casualties if not speed up diplomacy.