The recognition of Mu'awiya in Kufa, referred to as the "year of unification of the community" in the Muslim traditional sources, is generally considered the start of his caliphate.
With his accession, the political capital and the caliphal treasury were transferred to Damascus, the seat of Mu'awiya's power.
Syria's emergence as the metropolis of the Umayyad Caliphate was the result of Mu'awiya's twenty-year entrenchment in the province, the geographic distribution of its relatively large Arab population throughout the province in contrast to their seclusion in garrison cities in other provinces, and the domination of a single tribal confederation, the Kalb-led Quda'a, as opposed to the wide array of competing tribal groups in Iraq.
These long-established, formerly Christian Arab tribes in Syria, having been integrated into the military of the Byzantine Empire and their Ghassanid client kings, were "more accustomed to order and obedience" than their Iraqi counterparts, according to the historian Julius Wellhausen.
Mu'awiya relied on the powerful Kalbite chief Ibn Bahdal and the Kindite nobleman Shurahbil ibn Simt alongside the Qurayshite commanders al-Dahhak ibn Qays al-Fihri and Abd al-Rahman, the son of the prominent general Khalid ibn al-Walid, to guarantee the loyalty of the key military components of Syria.
Mu'awiya preoccupied his core Syrian troops in nearly annual or bi-annual land and sea raids against Byzantium, which provided them with battlefield experience and war spoils, but secured no permanent territorial gains.
Toward the end of his reign the caliph entered a thirty-year truce with Byzantine emperor Constantine IV (r. 668–685), obliging the Umayyads to pay the Empire an annual tribute of gold, horses and slaves.

Mu'awiya's principal challenge was reestablishing the unity of the Muslim community and asserting the credibility of the Caliphate and his own power across the provinces amid the political and social disintegration of the First Fitna.
There remained significant opposition to his assumption of the caliphate and a strong central government in general.
The garrison towns of Kufa and Basra, populated by the Arab immigrants and troops who arrived during the conquest of Iraq in the 630s–640s, resented the transition of power to Syria.
They remained divided, nonetheless, as both cities competed for power and influence in Iraq and its eastern dependencies and remained divided between the Arab tribal nobility and the early Muslim converts, the latter of whom were divided between the pro-Alids (loyalists of Ali) and the Kharijites, who followed their own strict interpretation of Islam.
The caliph applied a decentralized approach to governing Iraq by forging alliances with its tribal nobility, such as the Kufan leader al-Ash'ath ibn Qays, and entrusting the administration of Kufa and Basra to highly experienced members of the Thaqif tribe, al-Mughira ibn Shu'ba and the latter's protege Ziyad ibn Abihi (whom Mu'awiya adopted as his half-brother), respectively.
In return for recognizing his suzerainty, maintaining order and the forwarding of a relatively token portion of the provincial tax revenues to Damascus, the caliph let his governors rule with practical independence.
After al-Mughira's death in 670, Mu'awiya attached Kufa and its dependencies to the governorship of Basra, making Ziyad the practical viceroy over the eastern half of the Caliphate.
Afterward, Ziyad launched a concerted campaign to firmly establish Arab rule in the massive Khurasan region east of Iran and restart the Muslim conquests in the surrounding areas.
Not long after Ziyad's death, he was succeeded by his son Ubayd Allah.
Meanwhile, Amr ibn al-As ruled Egypt from the provincial capital of Fustat as a virtual partner of Mu'awiya until his death in 663, after which loyalist governors were appointed and the province became a practical appendage of Syria.
Under Mu'awiya's direction, the Muslim conquest of Ifriqiya (central North Africa) was launched by the commander Uqba ibn Nafi in 670, which extended Umayyad control as far as Byzacena
The recognition of Mu'awiya in Kufa, referred to as the "year of unification of the community" in the Muslim traditional sources, is generally considered the start of his caliphate. With his accession, the political capital and the caliphal treasury were transferred to Damascus, the seat of Mu'awiya's power. Syria's emergence as the metropolis of the Umayyad Caliphate was the result of Mu'awiya's twenty-year entrenchment in the province, the geographic distribution of its relatively large Arab population throughout the province in contrast to their seclusion in garrison cities in other provinces, and the domination of a single tribal confederation, the Kalb-led Quda'a, as opposed to the wide array of competing tribal groups in Iraq. These long-established, formerly Christian Arab tribes in Syria, having been integrated into the military of the Byzantine Empire and their Ghassanid client kings, were "more accustomed to order and obedience" than their Iraqi counterparts, according to the historian Julius Wellhausen. Mu'awiya relied on the powerful Kalbite chief Ibn Bahdal and the Kindite nobleman Shurahbil ibn Simt alongside the Qurayshite commanders al-Dahhak ibn Qays al-Fihri and Abd al-Rahman, the son of the prominent general Khalid ibn al-Walid, to guarantee the loyalty of the key military components of Syria. Mu'awiya preoccupied his core Syrian troops in nearly annual or bi-annual land and sea raids against Byzantium, which provided them with battlefield experience and war spoils, but secured no permanent territorial gains. Toward the end of his reign the caliph entered a thirty-year truce with Byzantine emperor Constantine IV (r. 668–685), obliging the Umayyads to pay the Empire an annual tribute of gold, horses and slaves.
Mu'awiya's principal challenge was reestablishing the unity of the Muslim community and asserting the credibility of the Caliphate and his own power across the provinces amid the political and social disintegration of the First Fitna. There remained significant opposition to his assumption of the caliphate and a strong central government in general. The garrison towns of Kufa and Basra, populated by the Arab immigrants and troops who arrived during the conquest of Iraq in the 630s–640s, resented the transition of power to Syria. They remained divided, nonetheless, as both cities competed for power and influence in Iraq and its eastern dependencies and remained divided between the Arab tribal nobility and the early Muslim converts, the latter of whom were divided between the pro-Alids (loyalists of Ali) and the Kharijites, who followed their own strict interpretation of Islam. The caliph applied a decentralized approach to governing Iraq by forging alliances with its tribal nobility, such as the Kufan leader al-Ash'ath ibn Qays, and entrusting the administration of Kufa and Basra to highly experienced members of the Thaqif tribe, al-Mughira ibn Shu'ba and the latter's protege Ziyad ibn Abihi (whom Mu'awiya adopted as his half-brother), respectively. In return for recognizing his suzerainty, maintaining order and the forwarding of a relatively token portion of the provincial tax revenues to Damascus, the caliph let his governors rule with practical independence. After al-Mughira's death in 670, Mu'awiya attached Kufa and its dependencies to the governorship of Basra, making Ziyad the practical viceroy over the eastern half of the Caliphate. Afterward, Ziyad launched a concerted campaign to firmly establish Arab rule in the massive Khurasan region east of Iran and restart the Muslim conquests in the surrounding areas. Not long after Ziyad's death, he was succeeded by his son Ubayd Allah. Meanwhile, Amr ibn al-As ruled Egypt from the provincial capital of Fustat as a virtual partner of Mu'awiya until his death in 663, after which loyalist governors were appointed and the province became a practical appendage of Syria. Under Mu'awiya's direction, the Muslim conquest of Ifriqiya (central North Africa) was launched by the commander Uqba ibn Nafi in 670, which extended Umayyad control as far as Byzacena 
Umayyad Caliphate