This is a controversial topic, so you may have multiple answers:
Answer 1: Yes
Muhammad did create and rule a large empire, both as a religious leader and a military leader. The term warlord is applicable.
Answer 2: NoProphet Muhammad (peace be upon him) is a model for all morals including war. However, he didn't wage wars for a personal benefit or glory. He put the rules during that no killing of a child. a woman, an old man, or an ill man. He ruled out that no cutting of a tree, no destruction of a house or a worshiping place. He occasionally lived only on dates and water for over three month as narrated by his wife Aisha. He didn't leave any fortune to his family after his death.
Accordingly, by the measures of a warlord, it couldn't be claimed that prophet Muhammad was a warlord but just a warrior with good morals.
Answer 3: You DecideThis is a volatile subject. Because Muhammad is the Jesus of Islam some people refuse to hear anything negative about him.
Whether he was a warlord may be a matter of opinion. During his ten years in Medina, Muḥammad personally commanded 27 military attacks. Prior to his death, he conquered most of the Arabian peninsula.
According to the dictionary a warlord is defined as:
"a supreme military leader"
You'll have to judge for yourself.
Answer 4: Definitional IssueWhether Mohammed fits into the definition of warlord depends more on the perception of warlords than it does with the actual nature of what Mohammed did. Warlords are typically seen as brutal leaders who control territories through the use of violence and galvanize their soldiers to terrorize any and all enemies. A warlord may be relatively decent as a person, but this is much rarer than warlords who are outwardly aggressive and belligerent.
Muslims ascribe to Mohammed a number of important virtues such as deference, impartiality, directedness, being respectful of differences among monotheists, and being discerning enough to tell truth from lies. These are not attributes typically ascribed to warlords, but to judges and sound political leaders. This is why Muslims often see Mohammed as a leader who happened to engage in warfare.
Mohammed, however, was no stranger to war. He commanded several major battles such as the Battle of Badr and the Battle of the Trench. He famously fought in these battles wearing two suits of armor. He also executed the supposed traitors in the Banu Qurayza Tribe of Medina for not supporting the Muslims in the battles with Mecca. He was a supreme tactician and very physically imposing figure. He had numerous wives and concubines and permitted the soldiers in his service to take wives from conquered territories as well. These attributes tend to fall well within what is considered to be a warlord.
So, whether Mohammed was a warlord or not depends on how you weight the definition of warlord.