The good jihaad is the jihaad of the one who strives against his own self (jihaad al-nafs) for the sake of Allah.
Allah Most High said:
{And whosoever STRIVES (JAAHADA), STRIVES (YUJAAHIDU) only for himself} (29:6). {As for those who STRIVE (JAHADU) in Us (the cause of Allah), We surely guide them to Our paths, and lo! Allah is with the good doers.} (29:69) This is a Meccan Sura and the two verses refer to Jihad al-Nafs. There was no military jihad then.
Without jihad of the nafs, fighting leads to Hellfire.
Allah Most High said:
{WA NAFSIN WA MAA SAWAAHA, FA-ALHAMAHA FUJURAHA WA TAQWAHA. QAD AFLAHA MAN ZAKAAHA WA QAD KHAABA MAN DAS-SAAHA}
“By the nafs and the proportion and order given to it, and its inspiration as to its wrong and its right; Truly he succeeds who purifies it, and he fails that corrupts it” (91:7-10). This is also a Meccan Sura.
Without purification, the nafs remains a “soul that enjoins evil” (al-nafs al – ammara bil-su’) until it surrenders itself in total obedience to the call of animal passions and shaytan.