Those who fight in obedience to Allah (swt) are the believers. Fighting in the cause of Allah (swt) is legislated to defend people and homeland, to protect the blood, honour and properties, it is not aimed to oblige people to convert to Islam:
فَمَن شَاءَ فَلْيُؤْمِن وَمَن شَاءَ فَلْيَكْفُرْ
(so whoever wills – let him believe; and whoever wills – let him disbelieve.) (Al-Kahf: 29)
(… وَالَّذِينَ كَفَرُوا يُقَاتِلُونَ فِي سَبِيلِ الطَّاغُوتِ…) (…, and those who disbelieve fight in the cause of Taghut..): The disbelievers fight in obedience to Satan, which represents oppression, pillaging of rights and properties and lives.
(… فَقَاتِلُوا أَوْلِيَاءَ الشَّيْطَانِ …) (…So fight against the allies of Satan…): The friends of Satan are the ones who made their companions all the elements of evil in this worldly life. Satan represents evil, there are creatures called Jinn, of which the infidel is called Devil, of course, as afore-mentioned, our inability to see the jinn does not mean their absence. There are creatures in the universe that do exist but we do not see them, as germs. So we are sure of their existence as long as Allah (swt) informed so.
( إِنَّ كَيْدَ الشَّيْطَانِ كَانَ ضَعِيفًا… ) (…Indeed, the plot of Satan has ever been weak): Certainly the plot of Satan no matter how it is, it is weak because it is based on false:
وَقُلْ جَاءَ الْحَقُّ وَزَهَقَ الْبَاطِلُ ۚ إِنَّ الْبَاطِلَ كَانَ زَهُوقًا
(And say, “Truth has come, and falsehood has departed. Indeed is falsehood, [by nature], ever bound to depart.”) (Al-Issra: 285)
But we must seek the help through patience, prayer, piety, and adherence to principles and putting them ahead of interests. In any society, the movement of hypocrisy emerges as it appeared in Medina. The hypocrites are:
مُّذَبْذَبِينَ بَيْنَ ذَٰلِكَ لَا إِلَىٰ هَٰؤُلَاءِ وَلَا إِلَىٰ هَٰؤُلَاءِ
(Wavering between them, [belonging] neither to the believers nor to the disbelievers.) (An-Nisaa: 143)
They put a foot here and another there and deal with the enemy of homeland as the hypocrites did in the age of the Prophet (saws). So we notice the truthfulness of the Holy Quran when applying the text to reality, this is normal because the Holy Quran is for every time and place and to be comprehended by intellectual.
The talk is about the oppressed among men, women, and children who could not leave Mecca to Medina, this is the revelation reason of the verse, but the specific reason does not disregard the general meaning and the more the intellect develops the more it takes from the Holy Quran what matches the recent time in which the man lives and benefits from the wisdoms