everyone will always hate you
I see this complaint a lot, but that hasn't been my experience.
In the game I'm playing right now, I'm playing as Saladin; huge map; 20 civs; Emporer level; just entered the early classical era.
From fairly early on I have maintained Victoria as a loyal friend. Brazil and I are on trading terms. France, India, and Egypt seem to be a bloc against Victoria and I.
Egypt and India declared an early mutual war against me. I opened my borders, paid some money and gave an extra resource to Victoria so that she would declare a mutual war against Egypt; Egypt being the only real threat to me. Victoria had 5 warriors near me and she used those warriors to enter my lands and fight Egypt's army, weakening it enough that my smaller army could mop up the rest. Danger averted; peace declared all around.
Later, seeing the Vikings expanding all over to the south of me, I knew I needed to strike quickly. So, I went full oligarchy, bee-lined to bronze working, and pumped out an army eventually totaling 5 warriors, 3 archers, 2 spearmen, 3 scouts, and 2 battering rams.
While the Vikings were busy fighting a city state in the East, I denounced them and renewed my declaration of friendship with Victoria. With my army assembled, I began moving on the Viking's nearest city, defended by 2 slingers and 4 warriors. The majority of their army was off fighting in the East. I couldn't see what sort of force they might have farther south in the capital.
I then paid a small amount of gold to Victoria to declare a mutual war against the Vikings. Her army would hold off the Vikings in the southwest while I concentrated on their core cities directly south. My eastern lands were exposed to the Vikings returning from their conquest of a city state in the East. I had to divide my army to protect my Eastern flank even as the other division took up defensive positions around the Viking's #2 city. After lots of fighting, I finally cleared the Eastern threat and was able to concentrate my army on taking the Vikings #2 city, which was far from certain at one point.
The Vikings brought up reinforcements from their capital in the south -- 2 warriors, 1 scout, and 2 slingers joined the fray -- inflicting much damage before their #2 city finally fell. The Vikings then retreated to their capital. My units survived, but badly injured.
So, that's where it's at, until I get home tonight. Victoria and I are loyal allies. Brazil and I are on good enough terms (even if the little angry face doesn't express it) and then there's some haters. Really fun game so far.