Mars is the planet which governs strength, action and on the extreme side i.e. war while Mercury is the planet of intellect, mind and mathematics in one’s behaviour in all walks of life.
A strong Mars may make a person aggressive, having leadership qualities and the will to do it – a man of actions; but if this is coupled with a weak Mercury governing the calculations and intellect, he may perform actions which are perceived as foolishly aggressive. A strong Mars with a strong Mercury brings forth a person who is balanced and leads a good life. Here again we need to have a holistic approach as the PATRA i.e. the vessel length and breadth of which is governed by Jupiter. The actions of a politician, bureaucrat, a businessman and for that matter every individual at each level depends on the play of these two planets – Mars and Mercury.
Mars, if strong, produces a Kshatriya (fighting instincts) and Mercury, a Vaish (businessman), and perhaps the caste system of today was in the past more from the perspective of putting a person in a profession towards which he by his inherent nature is aligned with.
In the present context, however, the morals and ethics have changed, which have to be borne in mind while studying a horoscope. A successful businessman today will perhaps have a weak Mars and a fairly strong Mercury. This is because a weak Mars connected with the house of business or self makes him to be a master deceiver, hits from the back and will not be straight forward. These qualities are evident in today’s Yuga but it may lead to problems in married life and perhaps have relations outside marriage if Venus is not strong.