Linked treaty documents
<p>A treaty <strong>T</strong> is signed by two state actors <strong>A1</strong> and <strong>A2</strong>.</p>

<p>It says:</p>

<blockquote>
  <ol>
  <li><p>Both sides agree to put in place a single customs territory (described herein) for an interim period of two years (described herein). </p></li>
  <li><p>Both sides will use best endeavours, in good faith, abiding by their respective legal orders, to negotiate the agreements referred to
  in declaration <strong>D</strong>.</p></li>
  </ol>
</blockquote>

<p>Declaration <strong>D</strong> (another document) says:</p>

<blockquote>
  <ol>
  <li><p>Both sides have agreed this declaration. This declaration accompanies <strong>T</strong>,
  that has been endorsed by <strong>A1</strong> and <strong>A2</strong>, subject to ratification.</p></li>
  <li><p>This declaration establishes the parameters for future economic cooperation between <strong>A1</strong> and <strong>A2</strong>, to take effect immediately after the interim period defined in <strong>T</strong>.</p></li>
  <li><p>For the period beginning immediately after the interim period defined in <strong>T</strong>, both sides agree to develop an economic partnership that builds on the single customs area defined in <strong>T</strong>.</p></li>
  </ol>
</blockquote>

<p>Are the agreements within <strong>D</strong> legally binding in international law? In other words, does the positioning of provisions in a separate document, linked with the "good faith" article, change things?</p>

<p>If the answer is <em>no</em>, if a new executive government is elected within <strong>A1</strong> on a platform that differs from <strong>D</strong>, by what legal mechanism could the agreements in <strong>D</strong> be reneged on? </p>

<p>The heart of my question is this: does the positioning of provisions in a separate document, linked with the "good faith" article, change the legally binding nature of the contents of the other document?</p>

<p>I realise that a country can simply walk away from a treaty obligation, but I am assuming that both states operate within the rules-based order as far as possible.</p>

<p>A treaty (or contract) spread across multiple documents is just as binding as one in a single document.</p>

<p>A treaty, once ratified, is enforceable by courts with relevant jurisdiction - these may be specific international courts/tribunals like the International Court of Justice or the Court of Arbitration for Sport or domestic courts in both/either country (treaties detail which).</p>

<p>Other answers have pointed out that there is no enforcement mechanism should a nation state choose to ignore such a judgement but there can be serious consequences to that state or its leaders - sanctions, seizure of foreign assets, travel bans etc.</p>

<p>In a practical sense there is no such thing as an agreement that is "legally binding in international law". Any nation can at any time renounce any treaty. The consequences are not some sort of international lawsuit. They are the loss of international reputation, lack of cooperation from the other party or parties to the renounced treaty, possible retaliatory action such as trade sanctions, and in an extreme case, military action.</p>

<p>Nations rarely renounce treaties arbitrarily, because doing so would make it harder to enter into other treaties, not because some legal mechanism prevents this.</p>

<p>In some cases membership in an international organization is conditioned on a nation adhering to some particular treaty or treaties, and a nation that does not do so may be expelled from the organization.</p>

<p>In the case described in the question, the government of A1 could send formal notice to A2 that it is renouncing D, and will not consider itself bound by it. It could do this after an election, or just a change of policy. It might be more likely to try to renegotiate D on terms more to its liking, but that is a policy and PR choice, not a legal requirement.</p>

international