Basically, ‘Ali (‘a) had more Shi‘ah and sympathizers from the ‘Adnanis from among the Qahtani tribes, and Shi‘ism among the Qahtanis had enormously expanded. The main Shi‘ah who constituted the historians and soldiers of the Commander of the Faithful (‘a) were Arab tribes from the south (Yemen) and Qahtanis. For instance, the Imam (‘a) thus said in Rajzi, one of the battle arenas in Siffin:

أنا الغلام القرشي المؤتمن الماجد الأبيض ليث كالشّطن
يرضى به السّادة من اهل اليمن من ساكني نجد و من اهل عدن)

I am a Qurayshi youth—trustworthy, great, pure, and like a lion—with whom the distinguished men of the people of Yemen from among the residents of Najd and ‘Aden are pleased.
Similarly, after the demise of the Prophet of Islam (S), most of ‘Ali’s (‘a) supporters among the companions of the Prophet (S) were Ansar who were Qahtani in origin, and constituted most of those who accompanied ‘Ali (‘a) from Medina up to the Battle of Jamal. In the same vein, when Imam al-Husayn (‘a) set off toward Kufah, ‘Abd Allah ibn al-‘Abbas said to him: If the people of Iraq like you and want to assist you, you write to them, “The enemy shall expel you from your city. Then, you come here.” Instead, you move toward Yemen where there are mountains, strongholds and forts that Iraq does not have. Yemen is a vast land and your father have Shi‘ah there. You go there and then send your preachers to the neighboring places to invite the people to come to you.
The companions of Imam al-Husayn (‘a), with the exception of Banu Hashim and some Ghaffaris, also belonged to Yemeni tribes. As Mas‘udi has said, “From among the companions of the Prophet (S), only four persons attained martyrdom at the lap of the Prophet (S) and these four were from the Ansar.”
The descent of the Ansar to Yemeni tribes is also obvious.
In contrast, the chiefs and nobles of Quraysh were hostile to ‘Ali (‘a) and his descendants (just as they were hostile to the Prophet (S)), while the sympathizers of the Imam (‘a) among them were few. Even the tribes that had close relations with the Quraysh, such as the tribe of Thaqif and the people of Ta’if who were supporters of Mu‘awiyah during and after the Battle of Siffin, had always been in the ranks of those who opposed ‘Ali (‘a).
For example, when Mu‘awiyah dispatched Busr ibn Artat to pillage the cities of Hijaz and Yemen, as Busr was approaching Ta’if, Mughayrah ibn Shu‘bah went to welcome him, saying: “May God give you pleasant reward! I heard the news of your harshness toward the enemies and benevolence toward the friends.” Busr said, “O Mughayrah! I want to put pressure on the people of Ta’if so as for them to pledge allegiance to the Commander of the Faihtful Mu‘awiyah.” Mughayrah said, “O Busr! Why do you want to do to your friends what you did to your enemies? Do not do it lest everybody turned into your enemy.”
There were also very few besides the Banu Hashim from among the Quraysh, such as Muhammad ibn Abi Bakr and Hashim Mirqal, who were on the Commander of the Faithful’s (‘a) side although from among the clans of Quraysh and opponents of ‘Ali (‘a), there were also some who accompanied him. For instance, Khalid ibn Walid was one of the Commander of the Faithful’s (‘a) adversaries, but his son, Muhajir ibn Khalid was among the soldiers of the Imam in the Battle of Siffin. Another case is that of ‘Abd Allah ibn Abi Hudhayfah, Mu‘awiyah’s maternal cousin, who was one of the sincere Shi‘ah of ‘Ali (‘a), and in the end attained martyrdom at the hands of Mu‘awiyah’s agents.
‘Ali (‘a) had followers and supporters from among all the Yemeni tribes such as the tribes of Kindih, Naka‘, Azd, Juhaynah, Himir, Bujaylah, Khath‘am, Khuza‘ah, Hadhramut, Mudhhaj, Ash‘ar, Tay, Sadus, Hamdan, and Rabi‘ah. But among them, the two tribes of Hamdan and Rabi‘ah were leading.
The Hamdanis who embraced Islam during the time of the Prophet (S), through ‘Ali’s (‘a) efforts, had always been sympathetic to him, and were considered as among the Imam’s sincere Shi‘ah. Mas‘udi says, “During the Battle of Siffin, not a single person from among them was in the army of Mu‘awiyah.”
Regarding Hamdan, ‘Ali has said:

ولو كنت بوّاباً على باب الجنّة لقلت لِحَمْدان أدخلوا بسلام

If I were the gatekeeper of paradise, I shall say to the tribe of Hamdan, “Enter in peace!”
Mu‘awiyah held a great grudge against the Hamdanis. One day during the Battle of Siffin, he went to the battle arena and recited this poem:

لا عيش الاّ فلق الهام من أرحب و يشكر شبام
قوم هم اعداء اهل الشام كم من كريم بطل همام
وكم قتيل و جريح ذام كذاك حرب السّادة الكرام

I shall not live unless I rip the heads of those of (the clans of) Arhab, Yashkar and Shabam (from the tribe of Hamdan).
They are people who are enemies of the people of Sham. So many of them are great, heroic and brave men.
So many they have killed, injured and handicapped. Yes, such is the battle of the gallant noblemen.
Then, by reciting this epic verse:

اللهم رب الحلّ والحرام لا تجعل الملك لاهل الشام

O Lord of hall and haram! Do not bestow the rule to the people of Sham, Sa‘id ibn Qays Hamdani attacked Mu‘awiyah while holding forward his spear, and Mu‘awiyah fled from him toward the center of the army of Sham. And he sent Dhu’l-Kala‘ (one of the commanders of Sham) to confront Sa‘d ibn Qays and the ensuing combat lasted till night. In the end, the people of Sham accepted defeat and fled. At this juncture, the Commander of the Faithful (‘a) recited this poem to encourage the Hamdanis:

فوارس من حمدان ليسوا بعزل غذاة الوغى من شاكر و شبام
يقودهم حامى الحقيقة ماجد سعيد بن قيس و الكريم محام
جزى الله همد ان الجنان فانهم سهام العدى في كلّ يوم حمام

Horsemen of Hamdan from (the tribes of) Shakir and Shabam do not slacken in the morning battle.
The advocate of truth and great man, Sa‘id ibn Qays, leads them. The kind people themselves shall also be protected.
May Allah grant the reward of paradise for (the tribe of) Hamdan as they are all arrows to the hearts of the enemies during battles.
As such, we can see poems composed by the army of Sham against Hamdan especially during the Battle of Siffin. For instance, ‘Amr ibn al-‘As addressed the tribe of Hamdan on one of the days of the Battle of Siffin, saying:

الموت يغشاه من القوم الانف يوم لهمدان و يوم للصّدف
و في سدوس نحوه ما ينخرف نضربها بالسّيف حتى ينصرف
و لتميم مثلها او يعترف

It shall receive death from this tribe; one day, Hamdan is victorious while another day it is just a shell.
The tribe of Sadus is also like them; as if it is not becoming old, but we shall strike them with the sword so as to restore the condition.
We shall treat (the tribe of) Tamim in the same manner, unless they confess submission.
A number of women of the tribe of Hamdan had also incited the supporters and soldiers of the Commander of the Faithful (‘a) during the Battle of Siffin against Mu‘awiyah. Among these women were Sawdah Hamdaniyyah and Zurqa’ Hamdaniyyah, daughters of ‘Addi ibn Qays. Sawdah addressed his father saying:

شعر كفعل ابيك يابن عمارة يوم الطّعان و ملتقى الاقران
وانصر عليّاً و الحسين و رهطه واقصد لهند و ابنها بهوان
ان الإمام اخا النّبي محمّد علم الهدى و منارة الإيمان
فقد الجيوش و سره امام لوائه قدماً بأبيض صارم و سنان

Given this, Mu‘awiyah nursed a grudge against them. And after the martyrdom of ‘Ali (‘a) they were summoned to Sham. They were asked to explain about their poems and they were reproached.
The second Yemeni tribe which had many Shi‘ah of ‘Ali (‘a) among its members was the tribe of Rabi‘ah. For example, in enumerating the Shi‘ah of ‘Ali (‘a) Burqa has allocated a certain part to the companions of ‘Ali (‘a) from the tribe of Rabi‘ah while allocating the rest of the Yemeni Shi‘ah in another part.
When ‘Ali (‘a) heard that a number of the tribe of Rabi‘ah in Basrah attained martyrdom at the hands of the army of ‘A’ishah, he said:

يا لهف نفسي على ربيعة ربيعة السّماعة المطيعة

I pity the Rabi‘ah, the obedient and submissive Rabi‘ah!
Mas‘udi also says, “‘Ali (‘a) had many talks about Rabi‘ah and eulogies to them because they were his helpers and supporters as well as his pillar among pillars.” Among ‘Ali’s (‘a) statements about Rabi‘ah is the poem below which he recited during the Battle of Siffin:

لمن راية سوداء يخفق ظلها إذا قيل قدمها حضين تقدماً
فيوردها في الصف حتى يعلها حياض المنايا تقطر الموت و الدّما
جزى الله قوماً قاتلوا في لقائه لدى الموت قدماً ما اعروا كرماً
واطيب أخباراً و اكرم شيمةً اذا كان اصوات الرجال تغمغما
ربيعة أعنى إنَّهم أهل نجدة و بأس إذا لاقو، خميساً عرمرما

The one who has the black banner and it is hoisted—once it is said to him to bring forward the banner, He will then join the ranks so as to bring forth the spears for death and blood drop from them.
May Allah bestow reward to the community that fought in the battle, welcomed death, and never opposed goodness.
They are the most well-dressed and beautiful-faced of people, when the voices of men at the battlefield are winded together.
I am referring to (the tribe of) Rabi‘ah. When confronting a huge army, they are brave and powerful.
It was one of the chiefs of Rabi‘ah, Jamil ibn Ka‘b Tha‘labi who was considered one of the Shi‘ah and supporters of ‘Ali (‘a). When he was captured by Mu‘awiyah, the latter told him: “Which blessing is greater than this that God made us prevailed over a man who within an hour killed a large number of our supporters!”
Shaqiq ibn Thawr Sudusi also said during the Battle of Siffin while addressing the tribe of Rabi‘ah: “O group of Rabi‘ah! Once ‘Ali is killed, there will be no excuse for even a single person from you to remain alive.” Also, after the death of Yazid, the people of Kufah expelled the Umayyad governor from their city and wanted to install somebody in his stead.
Some people suggested ‘Amr ibn Sa‘d to be the amir. Mas‘udi narrates that at that moment, the women of Hamdan, Kahlan, Ansar, Rabi‘ah, and Nakha‘ entered the central mosque. While weeping for Imam al-Husayn (‘a), they were saying: “Is it not enough that ‘Amr ibn Sa‘d killed Husayn and now he wants also to be our amir?”
With this statement, they made the people weep and persuaded them to abandon ‘Amr ibn Sa‘d.

Summary
Most of the supporters and Shi‘ah of the Commander of the Faithful were from the Qahtani and Yemeni tribes.
Among the companions of the Prophet (S), most of ‘Ali’s (‘a) sympathizers were from among the Ansar who had Yemeni origin.
Imam al-Husayn’s (‘a) main supporters were from among the Yemeni tribes, with the exception of the Banu Hashim and some Ghaffari men.
In contrast, the chiefs and nobles of Quraysh were inimical to ‘Ali (‘a), and his descendants and supporters among them were very few.
Among the Yemeni tribes, the two tribes of Hamdan and Rabi‘ah were leading in Shi‘ism.