If live male births out number female live birth for every decade since the 1930, why are females a majority?

it's a simple answer. War.

That's right. Now you need to visit an Insurance company and get the statistics about how males have a shorter life span than females.

Ola! It eventually balances out in the middle years and then females become a majority in later years.

Now, for the nitty gritty:

Originally, and still in most underdeveloped countries, there are more male infant deaths than female infant deaths.

Which balanced things pretty quickly.

However, in the United States, recently infant mortality is on the drastic decrease. (Due to pre-natal care, and post-natal care)

Wars

Men die younger and more often. There have been plenty of studies on this one. Some of it comes from having more hazerdous jobs or hobbies, they're less likely to get propper, timely healthcare. More men die in wars, also. I wish I had more detailed information, but try ask.com or something.

Because, once married men want to die.

Sorry, just kidding.

I believe the answer is actually due to deaths in the military and dangerous jobs historically held by men. As more women enter the military and do more dangerous work, we might just see the percentages change.

Men die faster, more dangerous activities, jobs, war, etc...

Did you ever hear of war? How many women are actully in the kill zone??