The last of the Persian strongholds was on the verge of being captured by the Muslims after the armies of ‘Umar Ibnul Khattab had brought the entire Persian empire to its knees.

Yazdajard, the last Persian emperor, sent a messenger with countless gifts to the emperor of China pleading for assistance against the Muslims.

Upon arrival, the emperor of China said to the messenger,

قَدْ عَرَفْتُ أَنَّ حَقًّا عَلَى الْمُلُوكِ إِنْجَادُ الْمُلُوكِ عَلَى مَنْ غَلَبَهُمْ، فَصِفْ لِي صِفَةَ هَؤُلاءِ الْقَوْمِ الَّذِينَ أَخْرَجُوكُمْ مِنْ بِلادِكُمْ، فَإِنِّي أَرَاكَ تَذْكُرُ قِلَّةً مِنْهُمْ وَكَثْرَةً مِنْكُمْ، وَلا يَبْلُغُ أَمْثَالُ هَؤُلاءِ الْقَلِيلِ الَّذِينَ تَصِفُ مِنْكُمْ فِيمَا أَسْمَعُ مِنْ كَثْرَتِكُمْ إِلا بِخَيْرٍ عِنْدَهُمْ وَشَرٍّ فِيكُمْ
“I do realise that kings must support other kings against their enemies, so please give me the description of these people (the Muslims) who've exiled you from your land. For you’ve told me that you outnumber them! This means that they’ve overcome you due to goodness which they possess and evil which you possess!”

Yazdajard’s messenger responded, “Ask me about them as you wish.”

The emperor of China asked, “Do they stick to their agreements with you?”

He responded, “They do”

The emperor asked, “What do they say to you before combat?”

He responded, “They offer us to accept one of three things. Either their religion, which if we accept, they will treat us just as they treat one another. Or the Jizya (tax for living as non-Muslims in Muslim land and to be exempt from military service) with their protection. The third option is combat.”

The emperor asked, “Tell me, are they obedient to those in authority amongst them?”

He responded, “They are the most obedient of people towards them”

The emperor asked, “Tell me, do they permit what their religion deems impermissible and forbid what their religion deems permissible?”

He responded, “No”

The emperor asked several other questions pertaining to their dress and what they ride to which Yazdajard’s messenger responded.

The emperor of China then wrote a letter and told the messenger to deliver it to Yazdajard. The letter said,

لَمْ يَمْنَعْنِي أَنْ أَبْعَثَ إِلَيْكَ بِجَيْشٍ أَوَّلُهُ بِمَرْوَ وَآخِرُهُ بِالصِّينِ الْجَهَالَةُ بِمَا يَحِقُّ عَلَيَّ، وَلَكِنْ هَؤُلاءِ الْقَوْمِ الَّذِينَ وَصَفَ لِي رَسُولُكَ صِفَتَهُمْ لَوْ يُحَاوِلُونَ الْجِبَالَ لَهَدُّوَها، وَلَوْ خلى سربهم أَزَالُونِي مَا دَامُوا عَلَى مَا وَصَفَ، فَسَالِمْهُمْ وارض منهم بالمساكنه، ولا تهجم مَا لَمْ يُهِيجُوكَ
“I am able to assist you with an army so huge that it starts from China and ends at your land in Persia. However I will not do this. This isn’t because I’m ignorant of my duties, but because the people whom you have described are people whom, if they want, can move *mountains* from their places! In fact, if they are given the opportunity, they will certainly remove me from my throne so long as they remain upon the descriptions that you’ve described.
My advice to you therefore is to make peace with them and agree to live with them. Do not attack them so long as they leave you alone”

(From Imam Tabari’s book, “Taareekhul Mulook”)

Subhan'Allah, it is just as you said, O Allah:

إِنَّ اللَّهَ لَا يُغَيِّرُ مَا بِقَوْمٍ حَتَّى يُغَيِّرُوا مَا بِأَنْفُسِهِمْ
"Allah will not change the condition of a people till they change the condition of themselves.. " (Al-Qur'an)