Treaties are agreements signed to spell out the terms and conditions to which the contractual parties have consented to abide by them. The terms and conditions should include remedies or damages or compensation for the injured party with which the agreement was broken. Often times, this would end up being a court battle to determine the injured party and the party in breach. There are valid reasons as well as invalid ones that caused the breach. For example, non-performance is one whereby one or both contractual parties had not performed according to the agreement. There is also a frustration reason, whereby a party would not be able to perform due to circumstances beyond the parties control, such as by a force majeure. For instance, a seller would not be able to satisfy the sales agreement of a house on the closing date because the house was burnt down by a fire the night before. Within the agreement, there are also terms that allow both parties to amiably terminate the agreement upon their wish, with the stipulation that advance notices must be given. Therefore, there are reasons for broken agreements in spite of their validity or justification.
With respect to the current question of broken agreements by the Federal government, the crown should honor the consultation framework in place with the aboriginals. However, this framework is only a skeleton of what needs to be done in terms of consultation process and procedure, which are not or may not be detailed in the agreement. Without putting these process and procedure in policy and in practice, there is a chance for the contractual parties to not follow the rules. A failure to live up to the terms of the agreement should not invalidate the agreement. In fact, the agreement or treaty would be good evidence of the performance required by the parties, and if a party is in breach, in this case, could be the Federal government, then the injured party should demand compensation for a broken treaty. Invalidity of a treaty or a demand for performance of a treaty should be judged by a court, which ideally is independent of the government. A treaty is signed for a reason, and that reason is to govern the behavior and performance of the contractual parties. A treaty should not be invalidated lightly without seeking recompense for the injured party through a court or exposing the problematic behavior. If that were the case, it would be a disservice to the public and businesses that rely on contractual law to help them achieve a promise in exchange for another contracted in the agreement. We have laws in a civil society to help people and businesses, or in this case the government, to negotiate the terms and conditions in an agreement or treaty and to which the contractual parties are bound. These laws hold the contractual parties to their promise and provide compensation for the one who abides by the agreement or treaty, and failure to live up to the agreement by a party is certainly deemed to be in breach by the same.
This is the definition of a treaty:
a : an agreement or arrangement made by negotiation: (1) : a contract in writing between two or more political authorities (such as states or sovereigns) formally signed by representatives duly authorized and usually ratified by the lawmaking authority of the state (2) : private treaty
b : a document in which such a contract is set down
When there is negotiation for an agreement or treaty, it is not unilateral, meaning not one sided. By all means, one party may be in a stronger position to negotiate with terms and conditions apparently more favorable, but this does not mean it is unilateral nor does it mean one party dictates all the terms and conditions. If that were the case, then this one party can just dictate, there is no need for an agreement or treaty. This one party might just as well set all the rules and punish those who are not following them, and this is call dictatorship.
You can still have an agreement/treaty and one or both parties might not follow through with it, but that does not mean it is a unilateral agreement/treaty. Both parties did sign and agree to the terms and conditions in the beginning so there is bilateral agreement/treaty. Things can happen during the period of the treaty that lead a party to breach the terms, but that does not mean the agreement/treaty is unilateral. You might not be able to contest it (in court or otherwise) due to circumstances such as financing or other terms, but that does not mean the agreement was made unilaterally by one party alone defining the terms and conditions.
In terms of city agreement in your example, there are agreements such as restrictive covenants and caveats that tie to the land and not the person. The terms of these agreements will be transferred to the new owner as they run with the land. However, usually these agreements (i.e. restrictive covenants) might have term limits, which means the agreement with the city on the covenants may end in 40-50 years then the owner can have that agreement (i.e. restrictive covenant) discharged from the land. These matters are related to municipal laws and property laws.
we're not debating history here. It already happened and circumstances and feelings at that time would perhaps be different from today. Regardless, we are only observers, and also are not historians. I thought the point of this debate is on the existence of an agreement/treaty, whether it was breached by non-performance, violence, etc. to render it invalid. If so, how should it be remedied going forward. Are there any remedies available? Not here to re-hash feelings or circumstances of the people from ages ago when the treaty was formed. It's more important to deal with the present situation and find remedies to improve the relationship and/or uphold or renegotiate a settlement.