The key was 'george' and the text was article 10 of the Geneva Convention relating to the treatment of POWs. (Actually, with my grid, the key is effectively 'hfpshf', when coding this I used a grid where A coded with A gave B, i.e. the whole thing was shifted up and left a bit. This does not matter when analysing.
One would have obtained the key length by comparing the message against a 'shifted' version of itself, and seeing how many letters match. There should have been an increase in matches with a shift of 6 letters. Thefore every sixth letter was encoded by the same key - in other words, every sixth letter was a Caesar Shift.
Every sixth letter could be gathered today, and the frequency of the occurence of the letters compared with English.
THEHI GHCON TRACT INGPA RTIES MAYAT ANYTI MEAGR EETOE NTRUS TTOAN ORGAN IZATI ONWHI CHOFF ERSAL LGUAR ANTEE SOFIM PARTI ALITY ANDEF FICAC YTHED UTIES INCUM BENTO NTHEP ROTEC TINGP OWERS BYVIR TUEOF THEPR ESENT CONVE NTION WHENP RISON ERSOF WARDO NOTBE NEFIT ORCEA SETOB ENEFI TNOMA TTERF ORWHA TREAS ONBYT HEACT IVITI ESOFA PROTE CTING POWER OROFA NORGA NIZAT IONPR OVIDE DFORI NTHEF IRSTP ARAGR APHAB OVETH EDETA INING POWER SHALL REQUE STANE UTRAL STATE ORSUC HANOR GANIZ ATION TOUND ERTAK ETHEF UNCTI ONSPE RFORM EDUND ERTHE PRESE NTCON VENTI ONBYA PROTE CTING POWER DESIG NATED BYTHE PARTI ESTOA CONFL ICTIF PROTE CTION CANNO TBEAR RANGE DACCO RDING LYTHE DETAI NINGP OWERS HALLR EQUES TORSH ALLAC CEPTS UBJEC TTOTH EPROV ISION SOFTH ISART ICLET HEOFF EROFT HESER VICES OFAHU MANIT ARIAN ORGAN IZATI ONSUC HASTH EINTE RNATI ONALC OMMIT TEEOF THERE DCROS STOAS SUMET HEHUM ANITA RIANF UNCTI ONSPE RFORM EDBYP ROTEC TINGP OWERS UNDER THEPR ESENT CONVE NTION ANYNE UTRAL POWER ORANY ORGAN IZATI ONINV ITEDB YTHEP OWERC ONCER NEDOR OFFER INGIT SELFF ORTHE SEPUR POSES SHALL BEREQ UIRED TOACT WITHA SENSE OFRES PONSI BILIT YTOWA RDSTH EPART YTOTH ECONF LICTO NWHIC HPERS ONSPR OTECT EDBYT HEPRE SENTC ONVEN TIOND EPEND ANDSH ALLBE REQUI REDTO FURNI SHSUF FICIE NTASS URANC ESTHA TITIS INAPO SITIO NTOUN DERTA KETHE APPRO PRIAT EFUNC TIONS ANDTO DISCH ARGET HEMIM PARTI ALLYN ODERO GATIO NFROM THEPR ECEDI NGPRO VISIO NSSHA LLBEM ADEBY SPECI ALAGR EEMEN TSBET WEENP OWERS ONEOF WHICH ISRES TRICT EDEVE NTEMP ORARI LYINI TSFRE EDOMT ONEGO TIATE WITHT HEOTH ERPOW ERORI TSALL IESBY REASO NOFMI LITAR YEVEN TSMOR EPART ICULA RLYWH ERETH EWHOL EORAS UBSTA NTIAL PARTO FTHET ERRIT ORYOF THESA IDPOW ERISO CCUPI EDWHE NEVER INTHE PRESE NTCON VENTI ONMEN TIONI SMADE OFAPR OTECT INGPO WERSU CHMEN TIONA PPLIE STOSU BSTIT UTEOR GANIZ ATION SINTH ESENS EOFTH EPRES ENTAR TICLE
Reformatted, the text looks like this:
The High Contracting Parties may at any time agree to entrust to an organization which offers all guarantees of impartiality and efficacy the duties incumbent on the Protecting Powers by virtue of the present Convention.
When prisoners of war do not benefit or cease to benefit, no matter for what reason, by the activities of a Protecting Power or of an organization provided for in the first paragraph above, the Detaining Power shall request a neutral State, or such an organization, to undertake the functions performed under the present Convention by a Protecting Power designated by the Parties to a conflict.
If protection cannot be arranged accordingly, the Detaining Power shall request or shall accept, subject to the provisions of this Article, the offer of the services of a humanitarian organization, such as the International Committee of the Red Cross, to assume the humanitarian functions performed by Protecting Powers under the present Convention.
Any neutral Power or any organization invited by the Power concerned or offering itself for these purposes, shall be required to act with a sense of responsibility towards the Party to the conflict on which persons protected by the present Convention depend, and shall be required to furnish sufficient assurances that it is in a position to undertake the appropriate functions and to discharge them impartially.
No derogation from the preceding provisions shall be made by special agreements between Powers one of which is restricted, even temporarily, in its freedom to negotiate with the other Power or its allies by reason of military events, more particularly where the whole, or a substantial part, of the territory of the said Power is occupied.
Whenever in the present Convention mention is made of a Protecting Power, such mention applies to substitute organizations in the sense of the present Article.