Murder

A similar element is present in warfare. Explains Scott Anderson in Harper's:

    I first went to war because I thought it would be exciting - and I was right. It is the most exciting thing I have ever experienced, a level of excitement so overwhelming as to be impossible to prepare for, impossible to ever forget.
    This attraction is not something to be discussed in polite company, of course. Yet I know I am hardly alone in my reaction. For a great number of people, and perhaps especially for those who traditionally have been called upon to wage it - young men - war has always been an object of intense fascination, viewed as life's ultimate test, its most awful thrill. Of all the easy, comfortable aphorisms that have ever been coined about war - that it is hell, that is tries men's souls - I suspect the odd utterance of General Robert E. Lee, made at the Battle of Fredricksburg in December 1862, may come closest to capturing the complicated emotions of those who have actually experienced it. "It is well that war is so terrible," Lee said, gazing over a valley where thousands of soldiers would soon die, "or we should grow to like it."

Some of the most basic reasons why people kill are not that unfamiliar: , thrill, gain, perceived social improvement, power, feelings of a greater guiding force telling them to do so. These are certainly elements in war, and they also rear their ugly heads in individual murders as well.

Still, the question of what causes some people to respond to the same urges differently has been a question of study, as currently encompassed in the field of criminology. An interesting breakdown of historical hypotheses can be found at one professor's site.

It seems that any number of things may cause people to lash out atypically, from poor parenting or difficulty integrating in society to a chemical defect, with some of the causes perhaps being related to each other. For example, researchers found that murderers' frontal lobes, which correspond essentially to the Freudian restraining superego, have lower glucose (sugar used when a portion of the brain is operating) uptake than normal people, independent of various other demographic factors.

The traits for criminals from serial killers to those responsible for genocide do not vary that much. However, there is even a great deal of debate over what made Hitler the way he was.

Here is the murder rate in some familiar countries

country	homicides	population	homicides / 100,000
MADAGASCAR	63	14303000	0.44
SYRIAN ARAB REP	174	13844000	1.26
JAPAN	1746	124793000	1.40
ENGLAND & WALES	726	51439203	1.41
EGYPT	871	57851000	1.51
HONG KONG	98	6061000	1.62
CYPRUS	12	734000	1.63
SINGAPORE	51	2930000	1.74
MOROCCO	472	26590000	1.78
CANADA	596	29248000	2.04
SCOTLAND	113	5132400	2.20
QATAR	12	540000	2.22
GREECE	298	10426000	2.86
TURKEY	1794	61183000	2.93
MALTA	11	364000	3.02
MAURITIUS	36	1154272	3.12
BELGIUM	343	10080000	3.40
SUDAN	1002	28947000	3.46
AUSTRIA	283	8031000	3.52
MARSHALL ISLANDS	2	54000	3.70
REP OF MACEDONIA	80	2142000	3.73
SLOVAKIA	205	5347000	3.83
CHILE	626	13994000	4.47
HUNGARY	477	10261000	4.65
AUSTRALIA	875	17931000	4.88
DENMARK	263	5205000	5.05
ITALY	3040	57193000	5.32
SLOVENIA	111	1942000	5.72
JORDAN	298	5198000	5.73
WESTERN SAMOA	10	164000	6.10
ISRAEL	389	5383000	7.23
ROMANIA	1732	22736000	7.62
INDIA	72543	918570000	7.90
CROATIA	367	4504000	8.15
AZERBAIJAN	667	7472000	8.93
UNITED STATES OF AMERICA	23330	260651000	8.95
PHILIPPINES	6338	67038000	9.45
REP OF MOLDOVA	414	4350000	9.52
UKRAINE	5008	51910000	9.65
COSTA RICA	298	3071000	9.70
BELARUS	1029	10355000	9.94
REP OF KOREA	4514	44453000	10.15
FINLAND	533	5095000	10.46
BULGARIA	948	8443000	11.23
SWEDEN	1050	8780000	11.96
KYRGYZSTAN	564	4596000	12.27
PANAMA	323	2583000	12.50
BERMUDA	8	63000	12.70
SAINT VINCENT&THE GRENADINES	16	111000	14.41
GEORGIA	788	5458000	14.44
LITHUANIA	560	3721000	15.05
KAZAKSTAN	2664	17027000	15.65
ZAMBIA	1456	9196000	15.83
ZIMBABWE	1779	11150000	15.96
LATVIA	412	2548000	16.17
ECUADOR	2073	11221000	18.47
NORTHERN IRELAND	341	1631822	20.90
RUSSIAN FEDERATION	34302	147997000	23.18
BOLIVIA	1687	7237000	23.31
NICARAGUA	1128	4401000	25.63
ESTONIA	385	1499000	25.68
JAMAICA	743	2496000	29.77
KUWAIT	940	1620000	58.02
COLUMBIA	27130	34520000	78.59
BAHAMAS	227	274000	82.85

Source: United Nations Crime and Justice Information Network, "United Nations Surveys of Crime Trends and Operations of Criminal Justice Systems," 1994 data.