We are already familiar that the word Kuja means the planet Mars (Mangala Graha). So the term, Kuja Dosha would mean a fault or trouble created by the planet Mars. Though Mars can create many types of problems in a chart, by it's lordship and placement, but Kuja Dosha actually refers to the problem created by Mars in respect of marital life. For the present time social structure, it creates problems in relationship as well.

Kuja Dosha is also called - Manglik , Manglik Dosha , Mangal Dosha , Bhauma Dosha etc.

Kuja Dosha is formed when Mars sits in specific houses in the Rashi chart. So he influences some particular houses by his placement and aspects. There are specific rules to check for Kuja Dosha while there are other factors which break or weaken this. Kuja Dosha is said to kill the spouse, but actually it does not happen this way always. Depending on the strength of the Dosha, it creates different scale or kinds of problems accordingly.

How the Dosha occurs - Conditions for forming Kuja Dosha

It is generally said that in a chart (Irrespective to male or female native) When Mars is found in any of the houses -  1, 4, 7, 8, 12 - Kuja Dosha forms. Some South Indian astrologers also take the 2nd house in addition - while most do not agree to this. (Mars in second can indicate bold or bitter speech, or using slang words etc.)

Mars is a planet of battle, war and fight. He is Tamasic in nature and belongs to the caste of warriors (Kshatriya). He in general is fond of fights, battles and is given to anger. That is why, very naturally, when he takes over the marital matters, he likes to put quarrel, fight and 'battle' in marriage, which disturb marital happiness. Mars is also he planet of over sex drive, too much boldness, and too fierce in nature - all of them are against a peaceful marriage.

The actual reason behind why these houses produce Kuja Dosha should be understood logically. That is why I am giving house by house explanation -

Mars in the 1st house - Mars is a planet of boldness, and kind of dictator in nature. That is why Mars in ascendant can make a person too bold, aggressive, or too dominating. He might want to be the all in all in his family, while not paying a good attention to what others (Or his spouse) are saying. He will be easily involved in fights and will express himself rather directly. He might be also of short temper. This causes the major problem.

Mars will also aspect the houses 4 (Happiness, family life), 7 (Spouse, married life) and 8 (Marital tie) and thus create problem in all these areas with ease. He will quickly create fights on unimportant issues.

Mars in the 4th house - The planet of battle is in the house of family life, so battle in family! Mars deprives the native from domestic harmony, there are misunderstandings among the family members. Mars will cast his 4th aspect on the 7th house of spouse and marital life. In 4th house Mars loses his strength for direction and creates more and more trouble in family life.

Mars in the 7th house - There will be clash and unhappiness in married life and this is perhaps the worst of all Kuja Doshas - a direct hit. Mars is a planet of abuse and violation and Mars being in 7th house very possibly can give violation in married life. In a female chart it might give physical or excessive mental torture from the husband. There will be also fight for the dominating power, and there might be lack of harmony in the sexual issues. The sexual and emotional needs of the partners might not match or might have a great difference. Mars might give over sexual desire / sickly sexual desire to the native or to his spouse and create mess in marital life for this issue. It might give a short tempered spouse.

Mars in the 8th house - The 8th house rules marital tie, from the 8th house we see the possibility of death of the spouse. Mars is the planet of accident, operation, assault from weapons and bleeding etc. - all of the things are ruled by 8th house. So being in the 8th house, Mars will be very eager to develop these tendencies. He might cause death of spouse, possibly through accident, operation or any other mishaps. Thus it can indicate an early death of the spouse. 8th house is also a house of hidden issues / immoral acts and Mars here can make the native / spouse be involved in hidden and sinful acts. When they come forward, storm blows in married life.

Mars in the 12th house - 12th house rules all kinds of losses and also the bed pleasure, i.e. sexual enjoyment. Mars here can give a native sickly desires, or illegal unions with other people. Again, Mars will aspect the 7th house with it's 8th aspect.

Counters to Kuja Dosha

There is no need to be really terrified if Mars is found in the houses 1/4/7/8/12. There are many facts that can counter or even nullify the Dosha. The most popular way to nullify this Dosha is to find a partner or spouse who has the same Dosha. It is believed that if both the partners have this Dosha, then the Dosha is nullified. Experience shows that this might be true.

However, there are certain facts in the chart itself that nullify the Dosha.

* Lordship is a very important fact here to consider. For the natives Cancer and Leo, Mars is very benefic being a Yoga Karaka. For natives Aries and Scorpio, for being the ascendant lord he will do good, on the other hand for ruling a Dusthana, he will not be purely benefic. For a Pisces native, he becomes the 9th lord as well as a mild killer (Maraka). However, Mars will undoubtedly produce strong Kuja Doshas to the ascendants he is a malefic for. (Virgo for an example.)

* According to Dr. B. V. Raman, Kuja Dosha nullifies in the following conditions -

a. If Mars is in 2nd house in any of the signs of Mercury, i.e., Gemini or Virgo.
b. If Mars is in 4th house in own sign, i.e., Aries or Scorpio.
c. If Mars is in 7th house in exaltation or debilitation, i.e., Capricorn or Cancer.
d. If Mars is in 8th house in any of the signs of Jupiter, i.e., Sagittarius or Pisces.
e. If Mars is in 12th house in any of the signs of Venus, i.e., Taurus or Libra.
 f. If Mars is in any house in Aquarius or Leo.

However, some hold the opinion that these conditions though weaken the Dosha, but does not completely nullify. I feel that it might be correct.

* The conjunction/aspect of other planets are very important facts. Jupiter is the most benefic planet in nature and will try to protect the native to it's best. A strong Jupiter can save the native from many of the havocs. Jupiter rules Dharma that is why he can propitiate Mars' anger and aggressiveness to a great extent. That is why a Jupiter (Esp. if strong) joining or expecting Mars will always fight against this Dosha. A benefic present with Mars in ascendant does not allow Mars to give the harsh nature too much, same applies to their Dristies (aspects) and also about other houses (4/7/8/12) as well.

The presence of Jupiter and/or Venus in the ascendant will work to protect from this Dosha. Moon joining Mars is also said to protect the native.

* Mars becomes matured at the age of 28 and that is why some suggest to wait till 28 years and then marry. This Dosha is said to be nullified after the age of 28. However, some do not agree to this point and suggest that this Dosha will remain active even after 28th year of the native, and will create problems in the periods of Mars, especially. This seem to be more logical to accept.

* Some astrologers also hold the opinion that Mars produces no Dosha in own sign or in exaltation sign. On the other hand some do not agree to this since being in own sign or in exaltation sign does not really make any difference in the nature but makes difference only in strength. I, personally, hold the latter view.

Conclusion

It has to be remembered that it is not only Mars that can create problem in married life, but there are a lot of other factors which can disturb marital happiness. That is why it will never be good to accuse a so called Kuja Dosha for marital disturbance. Other factors can greatly modify this Dosha both positively or negatively. While malefics join or aspect Mars, or hit the same houses hit by Mars, they surely worsen the condition. On the other hand benefics like Jupiter, Venus or Putra Adhipati / Dharma Adhipati (Lords of 5th and 9th houses) try to protect the things as per their strength. Praying to Lord Hanuman with Hanuman Chalisa and other Hanuman mantras, and prayers to Lord Kartikeya (Lord Skanda) protect the native from the evil of planet Mars. Angaraka Astottara Shata Namavali (The 108 names of Mars) can also be suggested. However, it would have to be remembered that each horoscope is unique so no remedy should be grossly suggested to all. The best is to get your chart checked by a knowledgeable Vedic Astrologer to know what remedy you would need to deal with this problem.