There is a very well-known Hadeeth:
عن عمران بن حصين قال قال رسول اهلل صلى اهلل عليو وسلم ال تزال طائفة من أمتي يقاتلون على الحق ظاىرين على من ناوأىم حتى يقاتل آخرىم المسيح الدجال
Hadhrat `Imraan ibn Husayn عنه هللا رضي narrates that Rasoolullaah هللا صلى وسلم عليه said: “There shall never cease to be a group from my Ummah fighting upon the Haqq, victorious over those who oppose them, until the last of them fight al-Maseeh ad-Dajjaal.” [Narrated in Sunan Abi Daawud.]
There are numerous other wordings of this Hadeeth narrated in other Kutub of Hadeeth, but what the reader will immediately glean from the words of this Hadeeth is that in every era, right until the emergence of Dajjaal, Allaah Ta`aalaa will let there be a group of Muslims on the surface of this earth who will be fighting (yuqaatiloon) upon the Haqq, and what that means is that first and foremost, they themselves are upon the Haqq. Then, they are fighting for the sake of the Haqq, fighting to defend the Haqq, fighting in the path of the Haqq, fighting to establish the Haqq.
Thereafter: “victorious over those who oppose them”. Regardless of the era the world is in, regardless of the situation, the circumstances, the difficulties, regardless of whatever level of military strength the Kuffaar possess, this Taa’ifah (Group) of Muslims will continue to be victorious against them. And, no matter what the Kuffaar try to do, regardless of the number of Crusades they wage against this Ummah, this Taa’ifah will never be wiped out. They will remain right up until the end, to have the opportunity to fight Dajjaal alongside the Mahdi and Nabi `Eesa السالم عليه.
In every era, Allaah Ta`aalaa will raise such people who will defend the Deen. In every era, Allaah Ta`aalaa will bring about people who will oppose the Kuffaar and stand victorious over them, their foot on the necks of the Kaafirs.
Each and every time the Kuffaar think that they will now succeed in obliterating Islaam from the face of the earth once and for all, Allaah Ta`aalaa will bring about such servants of His who will repel them and tramp them down, smashing their plots. This will never cease to be the case.