Here is some someting I have learned when I have played the game, I hope it will help:
As soon as you have made contact with the other civ's, and when you have got the writing tech, make embassy in their capital ats soon as possible. That will change their political stand against you fore a wile, and it will make it possible fore you to make an alliance.
Trade, trade and again trade with them. That will help you to reseach faster, it will make them pleased, and it's a key to make alliances if it's needed. If you are tecnological advanced, you are also the bos. It's easy to make a alliance if you have a tech to give away. In that way you can let your alllies fight fore you, and if you manage it correctly, you don't even need to engage your own troops(it's a good way to avoid disorder in your own cities). One tech it's a cheap way engage the others, since they all will lose more then that in a war, if the war continues fore a long time.
It will never be safe, no matter how large army you have. Belive me, I has been attacked even when I had 150 tanks. Some of the other civs like American, Zulu, Greece are agressive nations. They will attach you no matter how large army you have. Watch them, make an alliance with friendly nations wipe them out if you can, or if they act's treaty against you.
Finally, a simply rule, you must also have atleast one defender(spearman), in each of your cities that are bluild close up to your neighboers. If not, even India, the most kind nation in the game will attack you.