<a href="https://en.wikipedia.org/wiki/Frederick_II,_Holy_Roman_Emperor" id="mwIw" rel="mw:WikiLink" title="Frederick II, Holy Roman Emperor">Frederick II, Holy Roman Emperor</a>, is excommunicated by <a href="https://en.wikipedia.org/wiki/Pope_Gregory_IX" id="mwJA" rel="mw:WikiLink" title="Pope Gregory IX">Pope Gregory IX</a> for his failure to participate in the <a href="https://en.wikipedia.org/wiki/Crusades" id="mwJQ" rel="mw:WikiLink" title="Crusades">Crusades</a> during the <a href="https://en.wikipedia.org/wiki/Investiture_Controversy" id="mwJg" rel="mw:WikiLink" title="Investiture Controversy">Investiture Controversy</a>.<sup about="#mwt28" class="mw-ref reference" data-mw='{"name":"ref","attrs":{},"body":{"id":"mw-reference-text-cite_note-3"}}' id="cite_ref-3" rel="dc:references" typeof="mw:Extension/ref"><a href="./September_29#cite_note-3" id="mwJw" style="counter-reset: mw-Ref 3;"><span class="mw-reflink-text" id="mwKA">[3]</span></a></sup>
<span class="mw-reference-text" id="mw-reference-text-cite_note-3"><cite about="#mwt25" class="citation cs2 cs1-prop-foreign-lang-source" id="CITEREFEduard_Winkelmann1877">Eduard Winkelmann (1877), "<a class="extiw" href="https://de.wikipedia.org/wiki/s:ADB:Friedrich%20II.%20(Kaiser)" id="mwCnc" rel="mw:WikiLink/Interwiki" title="de:s:ADB:Friedrich II. (Kaiser)">Friedrich II. (Kaiser)</a>", <i id="mwCng"><a href="./Allgemeine_Deutsche_Biographie" id="mwCnk" rel="mw:WikiLink" title="Allgemeine Deutsche Biographie">Allgemeine Deutsche Biographie</a></i> (in German), vol.<span id="mwCno" typeof="mw:Entity"> </span>7, Leipzig: Duncker &amp; Humblot, pp.<span id="mwCns" typeof="mw:Entity"> </span>436–448</cite><span about="#mwt25" class="Z3988" id="mwCnw" title="ctx_ver=Z39.88-2004&amp;rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&amp;rft.genre=bookitem&amp;rft.atitle=Friedrich+II.+%28Kaiser%29&amp;rft.btitle=Allgemeine+Deutsche+Biographie&amp;rft.place=Leipzig&amp;rft.pages=436-448&amp;rft.pub=Duncker+%26+Humblot&amp;rft.date=1877&amp;rft.au=Eduard+Winkelmann&amp;rfr_id=info%3Asid%2Fen.wikipedia.org%3ASeptember+29"></span><link about="#mwt25" href="./Category:CS1_German-language_sources_(de)" id="mwCn0" rel="mw:PageProp/Category"/></span>