In The Name of Allah, The Most Merciful, The Bestower of Mercy.

Imam As-Sadi [may Allah have mercy upon him] said:

The Islamic Shariah has decided the issues of Siyaasah (see footnote a) in the most comprehensive manner and guided towards all that should be done when dealing with Muslims and others based on the best and most just system- combined mercy and strength in the affair, leniency and compassion, and mercy for the people whatever the circumstances may be. When that is not possible, force is employed prudently and justly, rather than injustice and violence. Allah [The Exalted] said:

إن الله يأمر بالعدل والإحسان وإيتاء ذي القربى وينهى عن الفحشاء والمنكر والبغي يعظكم لعلكم تذكرون وأوفوا بعهد الله إذا عاهدتم ولا تنقضوا الأيمان بعد توكيدها وقد جعلتم الله عليكم كفيلا

Verily, Allah enjoins Al-Adl (i.e. justice and worshipping none but Allah Alone – Islamic Monotheism) and Al-Ihsan [i.e. to be patient in performing your duties to Allah, totally for Allah’s sake and in accordance with the Sunnah of the Prophet in a perfect manner], and giving (help) to kith and kin (i.e. all that Allah has ordered you to give them e.g., wealth, visiting, looking after them, or any other kind of help, etc.): and forbids Al-Fahsha (i.e. all evil deeds, e.g. illegal sexual acts, disobedience of parents, polytheism, to tell lies, to give false witness, to kill a life without right, etc.), and Al-Munkar (i.e all that is prohibited by Islamic law: polytheism of every kind, disbelief and every kind of evil deeds, etc.), and Al-Baghy (i.e. all kinds of oppression), He admonishes you, that you may take heed. And fulfil the Covenant of Allah (Bai’a: pledge for Islam) when you have covenanted, and break not the oaths after you have confirmed them, and indeed you have appointed Allah your surety]. [Surah An-Nahl. Ayaat 90-91]

Allah commanded that justice be established with everyone, along with kindness and mercy for all, especially when it comes to family members and others whose rights must be upheld. In order to sanctify life (and physical well-being), wealth, honour, and rights, Allah forbade indecency and oppression. He also commanded the fulfilment and preservation of covenants and issued warnings against breaking them. Every Muslim is obliged to observe the commands and prohibitions (in the aforementioned verse), some of which are straightforward and evident; thus, there is neither a choice nor room for any dissent.

Allah [The Exalted] said:
وما كان لمؤمن ولا مؤمنة إذا قضى الله ورسوله أمرا أن يكون لهم الخيرة من أمرهم ومن يعص الله ورسوله فقد ضل ضلالا مبينا

It is not for a believer, man or woman when Allah and His Messenger have decreed a matter that they should have any option in their decision. And whoever disobeys Allah and His Messenger, he has indeed strayed in a plain error. [Surah Al-Ahzaab. Ayah 36]

Allah said:
فلا وربك لا يؤمنون حتى يحكموك فيما شجر بينهم ثم لا يجدوا في أنفسهم حرجا مما قضيت ويسلموا تسليما

But no, by your Lord, they can have no Faith, until they make you (O Muhammad ) judge in all disputes between them, and find in themselves no resistance against your decisions, and accept (them) with full submission]. [Surah An-Nisaa. Aayah 65]

Allah said:
فإن تنازعتم في شيء فردوه إلى الله والرسول

(And) if you differ in anything amongst yourselves, refer it to Allah (i.e. the Book of Allah) and His Messenger (i.e. go to the Messenger whilst he was alive and refer to his Sunnah after he has passed away]. [Surah An-Nisaa. Ayah 59]

Allah said:
وما اختلفتم فيه من شيء فحكمه إلى الله

And in whatsoever you differ, the decision thereof is with Allah (He is the ruling Judge)]. [Surah Ash-Shooraa. Ayah 10]

When this first affair is examined, you will find it to be in accordance with justice and wisdom, in harmony with the welfare of the people, and repelling corruption.

The second category consists of affairs whose origins or applications to reality are unclear, and unknown whether they are rejected or accepted by the Shariah, to be pursued or avoided. Regarding these affairs, they (i.e. the rulers, upright scholars, and experts) have been commanded to establish consultation, examine them from all angles, consider the (Shariah) criteria and regulations on which they are dependent, the goals and objectives that result from them, compare the welfare and disadvantages, and give preference to the most upright among them. Allah [The Exalted] said: [وشاورهم في الأمر – And consult them in the affairs]. [Surah Al Imran. Ayah 159]

And Allah stated about all the believers: [وأمرهم شورى بينهم – And they (conduct) their affairs by mutual consultation]. [Surah Ash-Shooraa. Ayah 38]

And with regard to this affair, Allah gave more room after laying the principles and rules that are appropriate for every period and location, regardless of how circumstances change and develop. The worldly and religious affairs, as well as the affairs of the people will be rectified, and evils and harms are repelled when the fundamental principles of the Shariah are applied to judge those affairs that are of a general nature and the side issues connected to them. However, to achieve this, it is necessary to convene councils of prudent individuals who provide true counsel –individuals of sound minds, broad intellect, sound opinion, and comprehensive understanding (that is in accordance with the Qur’an and Sunnah), so that internal issues are examined one by one, research that takes into account all relevant aspects is conducted, affairs are perceived as they should be, a clear understanding of what they depend on, the means to achieving them if they are to be pursued, a clear perception of the overall and partial benefits and welfare that will result from them, a study of the best and simplest ways to acquire them, a study of the harms that needs to be repelled and tracing their causes and sources of origin, resolving them as much as possible, striving to eliminate them completely if possible, but if not possible, at least reducing and lessening their evil outcomes. Allah [The Exalted] said: [فاتقوا الله ما استطعتم – Fear Allah as much as you can]. [Surah At-Taghaabun. Ayah 16] (1)

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Footnote a: What is Siyaasah: It refers to the regulation of civic affairs and has control over both the behaviour of the person and the entire society. It involves Islamic jurisprudence, which helps the rulers gain knowledge and comprehension of the Shariah laws and principles pertaining to managing the business of the state and its structures. [At-taleeq Alaa As-Siyaasah Ash-Shar’iyyah. Slightly paraphrased. Page 5 by Imam Muhammad Ibn Saaleh al-Uthaymeen (may Allah have mercy upon him)]

NB: This Siyaasah is to be differentiated from the methodology of ISIS, Ikhwaan Al-Muslimeen, and other deviated sects. Read articles by Shaikh Abu Iyaadh [may Allah preserve him]

http://www.ikhwanis.com/authors/Abu.Iyaad.cfm?start=31

http://www.shariah.ws/authors/Abu.Iyaad.cfm

[Ref 1: An Excerpt from Ad-Deenus Saheeh Yahillu Jamee al-Mashaakil (The right religion is the answer to every problem)-Page 12-13. slightly paraphrased]