Salamu Aleikum. Whoever denies islam is fighting islam. Is this correct?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Not everyone who disbelieves in Islam is belligerent non-Muslim fighting against Muslims or Islam. The Non-Muslims and the disbelievers are of various categories. Some of them are called Ahl Ath-Thimmah (non-Muslims living under Muslim rule), who are disbelievers residing in Muslim lands, with whom the Muslim ruler has conducted a Thimmah contract in return for paying the Jizyah. Another category is the Musta'man (non-Muslims who have entered the Muslim land and have been guaranteed safety) who are given safe access to Muslim lands for tourism or trade purposes. Another category is the Mu‘ahad (non-Muslims with whose people Muslims have a peace treaty), the disbelievers residing in their lands who have concluded covenants and peace treaties with Muslims. There is also the category of belligerent non-Muslims who are different from those mentioned above. The details regarding these categories and the relevant Sharee‘ah provisions can be learned from the books of Fiqh (Islamic jurisprudence).

Allah knows best.