wa alaykum salam wa rahmatullah,
This is a big topic, and quite easy to misunderstand, but I will try to keep it concise for the time, and add more to this answer in time in sha Allah.
Democracy is a man made system. Islam teaches us that the only system for humans is the Islamic one. This is from Allah, the most High. - From a creed basis, it is matter of disbelief for a Muslim to think that man-made laws and ideas which contravene the rulings from the Quran (Shari'ah) to be better/superior. Basically, if someone thinks that shariah should not be established, that it is not for today, they are committing a grave sin which can put them outside the fold of Islam.
At same time,
those Muslims who live and work inside non-Muslim lands, should respect the country they live in, and abide by the rule of law there. Islam teaches us to cooperate, be kind and good to people of other faiths and ideas, even if they hate Islam, even if they do not believe in God or are immoral, we still must treat them with fairness. - The other day I saw a sister speaking about a non-Muslim woman, accusing her of being naked and dressed like a "tart". This is not from the manners a Muslim should have, fortunately she is in a minority, but it does go to show how misled and even "arrogant" some Muslims can be. It is easy to be like that when you feel passionately about something and are trying to be stronger, but we must be careful of not going into extremes. The Prophet Muhammad
and his companions are our example, not our own emotions or ideas.
Back to your question, then according to Islam, the Muslim ruler should not be rebelled against. It is haram for Muslims to pick up arms and try to overthrow their Muslim ruler, even if he is a tyrant. This is established fact based on the Quran and Sunnah and many of the treatise of the early Muslims. Muslim rulers are not like "the pope". Whilst the disbelievers think the Pope to be infallible, Muslims know that their leaders can and do make mistakes and sin, sometimes terrible ones.
- Again, this opens a big debate and doors to those who begin making takfir of various rulers and accusing them of not being Muslim. The issue of rebelling was thus critisised much because of the bloodshed and problems stemming from it, especially when the people themselves are in a weak position.
Here is a fatwa by Shaykh Ibn Baz Rahimahullah:
There are people who think that because some of the rulers commit acts of kufr and sin, we are obliged to rebel against them and attempt to change things even if that results in harming the Muslims in that country, at a time when there are many problems in the Muslim world. What is your opinion?
Praise be to Allaah.
The basic comprehensive principle of sharee’ah is that it is not permitted to remove an evil by means of a greater evil; evil must be warded off by that which will remove it or reduce it. Warding off evil by means of a greater evil is not permitted according to the scholarly consensus (ijmaa’) of the Muslims. If this group which wants to get rid of this ruler who is openly committing kufr is able to do so, and can bring in a good and righteous leader without that leading to greater trouble for the Muslims or a greater evil than the evil of this ruler, then that is OK. But if rebellion would result in greater trouble and lead to chaos, oppression and the assassination of people who do not deserve to be assassinated, and other forms of major evil, then that is not permitted. Rather it is essential to be patient and to hear and obey in matters of good, and to offer sincere advice to the authorities, and to pray that they may be guided to good, and to strive to reduce evil and increase good. This is the correct way which should be followed, because that is in the general interests of the Muslims, and because it will reduce evil and increase good, and because this will keep the peace and protect the Muslims from a greater evil.
Majmoo’ Fataawa wa Maqaalaat Mutanawwi’ah li Samaahat al-Shaykh al-‘Allaamah ‘Abd al-‘Azeez ibn ‘Abd-Allaah ibn Baaz (may Allaah have mercy on him), vol. 8, p. 202
And Ibn Uthaymeen:
Is it obligatory to obey a ruler who does not rule according to the Book of Allaah and the Sunnah of His Messenger (blessings and peace of Allaah be upon him)?.
Praise be to Allaah.
The ruler who does not rule according to the Book of Allaah and the Sunnah of His Messenger should be obeyed in matters that do not involve disobedience towards Allaah and His Messenger, and it is not obligatory to fight him because of that; rather it is not permissible to do so unless he reaches the level of kufr, in which case it becomes obligatory to oppose him and he has no right to be obeyed by the Muslims.
Ruling according to anything other than that which is in the Book of Allaah and the Sunnah of His Messenger reaches the level of kufr when two conditions are met:
1.When he knows the ruling of Allaah and His Messenger; if he is unaware of it, then he does not commit kufr by going against it.
2.When what makes him rule by something other than that which Allaah has revealed is the belief that it is a ruling that is not suitable for our time and that something else is more suitable than it and more beneficial for people.
If these two conditions are met, then ruling by something other than that which Allaah has revealed constitutes kufr which puts a person beyond the pale of Islam, because Allaah says (interpretation of the meaning):
“And whosoever does not judge by what Allaah has revealed, such are the Kaafiroon (i.e. disbelievers)” [al-Maa’idah 5:44]. The authority of the ruler becomes invalid and he has no right to be obeyed by the people; it becomes obligatory to fight him and remove him from power.
But if he rules by something other than that which Allaah has revealed whilst believing that ruling by that – i.e. that which Allaah has revealed -- is what is obligatory, and that it is more suitable for the people, but he goes against it because of some whims and desires on his part or because he wants to wrong the people under his rule, then he is not a kaafir; rather he is a faasiq (evildoer) or a zaalim (wrongdoer). His authority remains, and obeying him in matters that do not involve disobedience to Allaah and His Messenger is obligatory, and it is not permissible to fight him or remove him from power by force or to rebel against him, because the Prophet (blessings and peace of Allaah be upon him) forbade rebelling against rulers unless we see blatant kufr for which we have proof from Allaah. End quote.
Majmoo’ Fataawa Ibn ‘Uthaymeen (2/118)
There were many people who fought for the right reasons in Afghanistan, as they had a Soviet invasion. Shaykh Jamil ur-Rahman who was a scholar and was killed there. The video you posted seems to be from the late 80s, before the take over of Afghanistan. Times have changed much from then.