I have held a trademark licence for 20 years and have recently had it cancelled by the owner of the trademark. It is my understanding that I did not breach any of the conditions. I am wondering if that is legal action by the owner to break the agreement without valid reason?
A license (trademark or copyright) may be permanent, for a fixed term, or cancelable at will or for cause by the rights-holder. If the terms provide that the license could only be canceled for cause then you might have a claim. If the terms were that it could be canceled at will, or had to be renewed on a regular basis, then the rights-holder would have been entitled to cancel. Without seeing the license agreement, there is no way to tell what it permits.
If the agreement did not specify, it is probably subject to cancellation at will, at least in the US. The law of the particular country may affect such default provisions. Trademark law, in particular, varies by country.