1. During the olden days, when women are taken as war captives, did the Muslim men take them as ‘what their right hand possess’ regardless of their beliefs ( i.e. pagans, Christians etc) or marital status (they were married women)?
2. if suppose a war happens nowadays, where an Islamic nation conquers another, and take the women as war captives, would they consider these women as what their right hand posess?
3. Are these women war captives just the women that are on the battlefield, or any women of the country conquered? Can you please kindly explain.

The captive who is owned is considered to be a fighting infidel, so it is not permissible to enslave the dhimmi, and it is the covenant between him and the Muslims.
And in the case of captivity, the woman becomes owned, whether she is married or not, and if her master wants to have intercourse with her, he waits for her to observe the ‘iddah of her husband’s water, then he can do that.
If the aggression of the infidels is against the Muslims, and the Muslims prevail, then it is permissible to take the women of the infidels, whether they are in the battlefield or not.