During His ten-years in Baghdád Bahá’u’lláh refrained from openly announcing any claim

Although Bahá’u’lláh had had the experience in the Black Pit of Tihrán…and felt a flood of spiritual power within him, He refrained at this time, and indeed for the whole of His ten-year stay in Baghdád, from openly announcing any claim. He decided instead to put his energies into reviving the fortunes of the Bábí community both in Baghdád and in Iran. He describes the situation of the Bábís at the time of his arrival thus: “Upon Our arrival in Iraq We found the Cause of God sunk in deep apathy and the breeze of divine revelation stilled. Most of the believers were faint and dispirited, nay utterly lost and dead.” Bahá’u’lláh began both to urge them to put away thoughts of revenge against the Shah and the clerics who had brought them so much suffering and to guide them towards manifesting in their lives the high ethical teachings to be found in the writings of the Báb. 

- Moojan Momen (‘Bahá’u’lláh, A Short Biography’)

Upon arrival in Baghdád Bahá’u’lláh found most “of the believers…faint and dispirited, nay utterly lost and dead”

Upon Our arrival in ‘Iráq We found the Cause of God sunk in deep apathy and the breeze of divine revelation stilled. Most of the believers were faint and dispirited, nay utterly lost and dead. Hence there was a second blast on the Trumpet, whereupon the Tongue of Grandeur uttered these blessed words: ‘We have sounded the Trumpet for the second time.’ Thus the whole world was quickened through the vitalizing breaths of divine revelation and inspiration. 

- Bahá’u’llah (‘Tablets of Bahá’u’lláh revealed after the Kitáb-Aqdas)

Upon taking residence in Baghdád Bahá’u’lláh encouraged Mirza Yahyá, his half-brother, who had already come to Baghdad, to return to Persia to serve the Faith of the Báb, as His ‘nominee’

When Bahá’u’lláh took up residence in Baghdád, where He would live for the next ten years, what had remained of the disconsolate, bewildered and decimated community of the Báb learned to turn to Him for advice, for guidance, for protection, because Mirza Yahyá, who was known as the ‘nominee' of the Báb, was nowhere to be seen. Having managed, as we have seen, to escape from Tákur in the company of his uncle, Mirza Zaynu’l-Ábidin, he was now living in Baghdád under the assumed name of Haji ‘Aliy-i-Lás Furúsh, in the street of the charcoal-vendors (Dhughál-Furúshán). It was Bahá’u’lláh's wish that he should return to Persia, there to serve the Faith of the Báb, as His own words make clear:

“About two months after Our arrival in Iraq, following the command of His Majesty the Shah of Persia -- may God assist him -- Mirza Yahyá joined Us. We said unto him: "In accordance with the Royal command We have been sent unto this place. It is advisable for thee to remain in Persia. We will send Our brother, Mirza Musa, to some other place. As your names have not been mentioned in the Royal decree, you can arise and render some service." Subsequently, this Wronged One departed from Baghdad, and for two years withdrew from the world. Upon Our return, We found that he had not left, and had postponed his departure. This Wronged One was greatly saddened. God testifieth and beareth Us witness that We have, at all times, been busied with the propagation of this Cause. Neither chains nor bonds, stocks nor imprisonment, have succeeded in withholding Us from revealing Our Self.” (Baha'u'llah, ‘Epistle to the Son of the Wolf’) 

- Hasan Balyuzi (‘Bahá’u’lláh King of Glory’)

City of Baghdád and its pivotal role in Bahá’u’llah’s Revelation

In that city, described in Islamic traditions as “Ẓahru’l-Kúfih,” designated for centuries as the “Abode of Peace,” and immortalized by Bahá’u’lláh as the “City of God,” He, except for His two year retirement to the mountains of Kurdistán and His occasional visits to Najaf, Karbilá and Káẓimayn, continued to reside until His banishment to Constantinople.

• To that city the Qur’án had alluded as the “Abode of Peace” to which God Himself “calleth.”
• To it, in that same Book, further allusion had been made in the verse “For them is a Dwelling of Peace with their Lord … on the Day whereon God shall gather them all together.”
• From it radiated, wave after wave, a power, a radiance and a glory which insensibly reanimated a languishing Faith, sorely-stricken, sinking into obscurity, threatened with oblivion.
• From it were diffused, day and night, and with ever-increasing energy, the first emanations of a Revelation which, in its scope, its copiousness, its driving force and the volume and variety of its literature, was destined to excel that of the Báb Himself.
• Above its horizon burst forth the rays of the Sun of Truth, Whose rising glory had for ten long years been overshadowed by the inky clouds of a consuming hatred, an ineradicable jealousy, an unrelenting malice.
• In it the Tabernacle of the promised “Lord of Hosts” was first erected, and the foundations of the long-awaited Kingdom of the “Father” unassailably established.
• Out of it went forth the earliest tidings of the Message of Salvation which, as prophesied by Daniel, was to mark, after the lapse of “a thousand two hundred and ninety days” (1280 A.H.), the end of “the abomination that maketh desolate.”