Breaking treaties with disbeliever states is the responsibility of the Muslim rulers and scholars.

Question:
Does the treaty and covenant between us and a disbeliever state lapse if it aggresses against one of the Islamic states, and what is the legal criterion for this?

Answer:
Answer: This has specific criteria, and it is among the affairs of the Muslim rulers who examine it. It is not for every individual to rule on this. If a disbeliever state with which a treaty exists breaks the covenant, it is to be fought, because the treaty is what prevents fighting them. Or if they support the allies of the Muslims, even if the allies of the Muslims are disbelievers: if one allies with the Muslims under the authority of the Muslim ruler, and a state aggresses against him, it is obligatory to fight it to preserve the covenant. This is because the Quraysh made a truce with the Prophet (peace and blessings be upon him) during the Expedition of Hudaybiyyah. Khuzaa'ah entered into the alliance of the Messenger of Allah (peace and blessings be upon him), and Banu Bakr entered into the alliance of the Quraysh. It was obligatory upon the Messenger (peace and blessings be upon him) not to aggress against the allies of the Quraysh, and it was obligatory upon the allies of the Quraysh not to aggress against the allies of the Messenger of Allah (peace and blessings be upon him). So when Banu Bakr aggressed against the allies of the Messenger, who were Khuzaa'ah, their covenant was broken. The Messenger of Allah (peace and blessings be upon him) then marched to Mecca and conquered it in the Year of the Conquest. This is the known methodology. The breaking of a covenant has causes that must be known and studied, and those who undertake this are the rulers and the scholars, not the common people.