Odo may have entered into a pact with Conan's maternal uncle, Hoel, Count of Nantes, with the goal of dividing Brittany between them.

Being under threat of rebellion in Nantes, sponsored by Geoffrey VI, Count of Anjou, Hoel could not send Odo any aid.

Henry II of England, the Count of Anjou, attempted to obtain control of the Duchy of Brittany, which neighboured his lands and had traditionally been largely independent from the rest of France, with its own language and culture.

Henry II, responded by seizing the Earldom of Richmond, Conan's paternal inheritance, and demanded the return of Nantes.

[13] While local Breton nobles began to rebel against Conan IV, Henry had begun to alter his policy of indirect rule in Brittany and started to exert more direct control.

Conan is usually remembered in Breton historiography as a weak ruler, unable to protect his duchy against the powerful Angevin king,[17] although historian Eric Borgnis-Desbordes has recently qualified this opinion.

[18] Conan IV is mentioned in the tragedy Jean sans Terre ou la mort d'Arthur (1791) by Jean-François Ducis, the novels Time and Chance (2002), Prince of Darkness (2005) and Devil's Brood (2008) by Sharon Kay Penman, and the second volume of the trilogy Le Château des Poulfenc (2009) by Brigitte Coppin.