When Mars is placed in first , fourth, seventh, eighth and twelth house than it makes the Manglik dosha. Mars is a planet that represents fire. It causes a dosha in the chart because it tends to burn the relationship between a husband and wife; causing rift, tensionsMars influences the fourth, seventh and eighth house from the place where it is situated.

Mangal in first house affects 4th, 7th and 8th house which represent happiness, partnership  and marital bond respectively. This position of Mars makes such jatak very vulnarable for anger which becomes the cause for disturbed married life.

Fourth house placed Mars influence the 7th, 10th and 11th house which are responsible for relation with spouse, job and benefits from the work sequentially.In this situation Mangal creates unnecessary household issues which leads to unhappiness of mind. This eventually affects the other mentioned areas of life.

Seventh house located Mars keeps hold on 10th, 1st and 2nd house. This Mars makes person extra energetic. This mars creates some or other health issues oftenly which becomes the reason of disharmony between husband and wife.

When mars is stationed in eighth house it makes a person anxious and extravagant. Person loses the opportunities which can make his married life and other relations better. 

Mars in twelth house compels a person to do activities which are short lived or unpurposeful due to agile nature. aspect 3rd house, 6th house (debts, disease, competition) and 7th house. This person is also troubled with the enemies.

Please remember that there are some exceptions to Manglik dosha which only an astrologer can implement. The second important thing that correction of this dosha is mandatory before marriage. Remedies are decided only after proper horoscope analysis.