Is it mandatory for an Islamic state to enforce Islam in the neighbouring state, once a capable enough power is achieved, or to otherwise ask the neighbouring state to pay Jizya? The Question arises since Islam teaches us that religion is not to be enforced on anyone. Could you answer this apparent contradiction?
To require the neighbouring states to surrender themselves before Islam was only a part of the mission of the companions of the Prophet (the Sahaba), radhiallaho anhum. We can only preach our religion to others, and if there is persecution in a neighbouring country, it’s only then that we are expected to do Jihad to rescue the weak people from a tyrannical rule. Since the companions of the Prophet, Allah’s mercy be on him, were able to establish a society that could claim to be an ideal religious one, they were able to do what is known as ‘itmam-e-hujjah’, presentation of the truth in a manner that the disbelievers have no rational grounds to reject. Thus, they had the moral justification to ask the neighbouring rulers to either submit to Islam, or let Muslims rule over them, or be prepared for a war. No other group after them can do that. Wallahu ‘Alamo Bithawab (and Allah knows best).