Complex sentence: Not all signatories of the Treaty of Sèvres were parties to the Treaty of Lausanne, nor was there a valid international act of annulment of the Treaty of Sèvres.
Split into simpler sentences: Not all signatories of the Treaty of Sèvres were parties to the Treaty of Lausanne. Nor was there a valid international act of annulment of the Treaty of Sèvres.