I’m not sure I’d even go so far as to say “fewer”.
In the past, wars may have been fought because leaders just could not contain their aggression. Such wars may well be “less” if there were only women, because women, as a group, are somewhat less aggressive than men.
These days, wars are most often fought because of historic ethnic or nationalist grievances, because of ideological conflicts, to preserve or overthrow a balance of power, out of other types of perceived national self-interest, or even as a sort of systemic failure (think WW1); personal aggression on the part of leaders plays little part.
Moreover, there is a certain self-selection that goes on in people becoming leaders. Those who rise to such positions tend to be ambitious, dynamic and forceful (whether for good or bad!). I see no reason why, if such leaders were chosen from women only, they would be significantly less likely to pursue nationalist grievances, ideological differences, etc. using the tool of conflict (conflicts that, as leaders, they probably won’t personally fight in).
The pattern I’m thinking of is leaders of major corporations. In the past these were typically all men. Now, there are a fair number of women, and one can confidently look to a future in which men and women will be more-or-less equally represented in the highest leadership roles in business. Has business changed much thereby? No - because the goals of business (maximize shareholder profits) remain unchanged; the leaders who rise to such positions, men and women, are self-selected as those capable of maximizing shareholder profits.
Women as a generality may (or may not) be more caring and compassionate and all other good traits than men as a group - but the individual women who become business leaders are self-selected as those capable of generating maximum shareholder profits.
Likewise, women national leaders.
