Can someone translate the question below to English for me. I will answer the question on my own, I just need to understand what it is asking me? Thank you!!!!

¿Qué decía el Tratado de Guadalupe Hidalgo sobre lo que debería pasar con los ciudadanos mexicanos de lo que había sido México antes de firmarse el Tratado?

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The question is asking what the Treaty of Guadalupe Hidalgo stated regarding what should happen to Mexican citizens of what had been Mexico before the Treaty was signed. To translate the question, you can use an online translation tool or consult someone who is fluent in both Spanish and English.