Historically, the armies of the Mlecchas, Asuras, and Rakshasas after defeating the army, killing the king, and conquering a city, would kill all the civilian men, rape all the women, make their children their slaves, loot all the property and wealth, and burn the remains of the city.
9 The Israelites captured the Midianite women and children and took all the Midianite herds, flocks and goods as plunder.
10 They burned all the towns where the Midianites had settled, as well as all their camps.
11 They took all the plunder and spoils, including the people and animals
Now what is important is the next part:
13 Moses, Eleazar the priest, and all the leaders of the community [the Israelite assembly] went to meet them [the Israelite warriors] outside the camp.
14 Moses was angry with the officers of the army—the commanders of thousands and commanders of hundreds—who returned from the battle.
15 “Have you allowed all the women to live?” he asked them.
17 Now kill all the boys. And kill every woman who has slept with a man,
18 but save for yourselves every girl who has never slept with a man.
So here we have one of the earliest recorded mentions of women being considered spoils of war as well as a religious sanction of kidnapping virgin girls in warfare and making them wives.
Is this allowed as per Hindu, Kshatriya Dharma?
The Manusmriti says this:
7.96 - Chariots and horses, elephants, umbrellas, wealth, grains, animals, women, all goods and baser metals belong to him who wins them.
rathāśvaṃ hastinaṃ chatraṃ dhanaṃ dhānyaṃ paśūn striyaḥ | sarvadravyāṇi kupyaṃ ca yo yaj jayati tasya tat
However, the commentators don't say anything about the mention of women.
There is also a form of marriage permitted by Hindu texts that only Kshatriyas can do, called the Rakshasa Vivaha, or the Kshatra Vivaha, in which the girl is won through fighting. It is named after Rakshasas because this form of marriage is characteristic of them.
Manu 3.33 - The forcible abduction of the maiden from her home, while she is crying out and weeping, after having beaten and wounded and pierced [her guardians],—is called the “Rākṣasa” form.
Āpastamba-Dharmasūtra (2.12.2).—‘When the girl is taken away after attacking her guardians, it is the Rākṣasa.’
Vaśiṣṭha (1. 34).—‘When they suddenly attack with force and take away the girl, it is the Kṣātra form of marriage.’
Hārīta (Vīramitrodaya-Saṃskāra, p. 856).—‘It is the Rākṣasa form of marriage when, with the king’s support, the girl is obtained by attacking and chastising her guardians.’
Āśvalāyana- Gṛhyasūtra - 'He may carry her off, killing (her relatives) and cleaving (their) heads, while she weeps and they weep: this (is the wedding called) Râkshasa.'
However, I don't think it refers to all women because caste restrictions and adultery rules would still apply, so that Kshatriyas can't abduct Brahmin girls because they are of a higher caste than him and can't abduct Vaishyas or Shudra women because they cannot do a Rakshasa vivaha, and the Kshatriyas also cannot abduct women who were already married to another man, even if she is a widow, and even if she is the widow of a warrior that was slain by him, because that would be adultery.
So I think the mention of "women" as spoils of war in the Manusmriti verse refers to unmarried, Kshatriya, virgin girls whose fathers were slain in the battle.
Do any scriptures or commentaries talk about this?