most lethal battles
... that three of the most lethal battles involving the United States military saw more than 20,000 soldiers killed?
... that three of the <b id="mwBSs"><a class="mw-redirect" href="./List_of_most_lethal_American_battles" id="mwBSw" rel="mw:WikiLink" title="List of most lethal American battles">most lethal battles</a></b> involving the <a href="./United_States_Armed_Forces" id="mwBS0" rel="mw:WikiLink" title="United States Armed Forces">United States military</a> saw more than 20,000 soldiers killed?