[quote=Rare]
Prussia might of defied the ToC. Not the Netherlands, because they didn't sign the treaty at the time.
[/quote]

Prussia didn't defy the ToC. Even if we ignore whatever secret aspects of the treaty (which Pasta has recently confirmed the existence of) would absolve them of guilt for Belgium, they're ToC's 'neutral mediators' in Europe, as per the publicly displayed Article 2.

[quote=Treaty of Constantinople, Article 2] It is hereby recognised by all the signatories that the Kingdom of Prussia and the Austrian Empire shall act as neutral mediators in Europe when war threatens to erupt, and will do all in their power to uphold Article 1.[/quote]

Prussia mediated a conflict by intervening in the Dutch-Belgian dispute, acting in accordance with ToC. If Brazil doesn't think Prussia's involvement was legitimate, Brazil's dispute is with the ToC, not Prussia.