A planetary war, or graha yuddha, occurs in a chart when two planets (other than the Sun, Moon, Rahu. and Ketu) are within 1 degree of one another. This is a controversial topic in Vedic astrology because there are conflicting methods given, in both modern and classic texts, for determining which planet wins the war and what the effects are.
The following is an infamous case of planetary war in the chart of Adolf Hitler. In his 7th house in the sign of Aries, Venus and Mars are in a planetary war. Venus is at 24 degrees 22 minutes longitude and Mars is at 24 degrees 4 minutes. A commonly held method for determining who wins is to proclaim the planet with the lowest degrees or longitude the winner. In this case Mars would win, which is said to give strength to the winning planet and weakens the losing planet.
Hitler's Natal Chart
In Hitler's early life he aspired to be an artist, represented by Venus, but failed miserably. He later became an absolute dictator by force, and the epitomy of a war monger, represented by Mars. He never married but did claim in speeches that the reason for this was because he was "married to the German people." In any case, let's just say he wasn't a very romantic or affectionate person. After all, he was responsible for death of over 30 million people! For these reasons, it does make logical sense that Mars won the war, grew in strength, and Venus lost and was weakened.
It should be noted that Venus is also closely aspected by Saturn in addition to being conjunct with Mars. Mars additionally increases in strength due to being in a ruchaka mahapurusha yoga. Both Mars and Venus are involved in multiple raja yogas and dana yogas with Mercury, the Sun and Saturn. These are factors that do play into the effect of Mars and Venus.
Another method for determining who wins the war is to see which planet is the most northerly. That planet will win the war according to some texts. Some say that this refers to latitude while others say that this refers to declination. Some software programs, like Sri Jyoti Star, will give latitude and declination along with degrees or longitude. Panchanga's or Indian ephemeris's will also give these calculations, but not western ephemeris's typically. According to latitude, Venus is at 6 degrees 20 minutes and Mars is at 0 degrees 9 minutes. Venus wins the war. In terms of declination, Venus is at 22 degrees 54 minutes, while Mars is at 16 degrees 54 minutes. Venus again wins the war. Another method is to give the planet with brighter rays the status of victor. In this case, Venus always wins.
Planetary war is a area that should be researched. It's confusing that there are so many opinions about it. One thing that I appreciate about K.N. Rao's approach to Vedic astrology is that he relies on practical research, and hard core results, not dogma. If a method or principle given in classical texts doesn't work based on your experience with a series of charts then don't use it.
For more detailed information on planetary war see yesterday's article: Conflicting Views of Planetary War.