Planet Mars or Mangal situated in 1st, 4th, 7th, 8th or 12th house makes a person’s birth chart or Kundli to be called Manglik. This is also known as Mangal Dosha. Roughly, of all persons, 42% are supposed to be Manglik.
Many astrologers have spread a false belief that Mangal Dosha can have negative effects on a person's marital life, including conflicts, misunderstandings, and even divorce. Few astrologers also suggest that Mangal Dosha is resolved once a person attains 28 years of age which is not true.
A Manglik person has their birth chart influenced by Mars which makes them stubborn. They often times possess a belief that whatever done by them is always correct. When corrected by someone, they spend much of their time arguing and convincing others that they are in the right and may sometimes get annoyed or angry at those who attempt to prove them wrong. This characteristic is due to the influence of Mars.
In case of spouses in a marriage, the spouse with Manglik Kundli will tend to be more dominant while the Non-Manglik spouse may tend to get exhausted or feel defeated dealing with the other spouse’s behaviour. When such Non-Manglik spouse cannot bear with the behaviour of their Manglik spouse, it may cause marital issues and may lead to separation.
The other reason behind this which has been observed throughout our experience is that when an individual’s birth chart is influenced by Mars, they possess a greater sex drive compared to those with Non-Manglik birth chart or Kundli.
Therefore, if both the spouses in the marriage have a Manglik birth chart influenced by Mars, it brings a balance between the two in terms of libido. In a situation where one spouse’s birth chart is influenced by Mars and the other spouse’s birth chart is not, there is a difference in libido between the two. This often times cannot be explained to others including members of both families and as a result, the spouses often consider other reasons to separate from each other.
It is also necessary to observe the 7th house planet which represents spouse and 4th house planet which represents Lagna Sukh or Harmony in Marriage, Nakshatras along with position of Mars while matching Kundlis before marriage.
This is a general observation based on reading numerous birth charts of married individuals from diverse backgrounds.
