AI will look at your provinces, and if they seem to be weak it attacks you. You should have provincial defence of 11 in your border provinces, and often that is enough to make the AI conquer independets until it cannot reach them anymore. 11 is better than 10, because IIRC AI cannot make out the difference between 1 and 10, or 11 and 20. And between 21 and 30, but 21 would be too expensive in almost all cases...
And the reason your hoplites can't hit the dryads is their Awe ability. Click the icon of that ability, and it should tell what Duncanish just said. Hypaspists have higher morale, and will do much better. Against Awe +0 units with morale of 10 have 50% change of success. Against Awe +2 50% would take morale 12.
This is from Saber Cherry's old thread
Dominions Dice Roll Chart.
Hypaspist has morale of 14, and Dryad Hoplite has Awe+0. If 2d6 open-ended roll is used, as for most things in Dominions, the Hypaspist has to score a differential roll over (10-14), or over -4. From row -5+ (-5 or more), wee see that the probability of a Hypaspist getting through Dryad Hoplite's Awe would be 86%.
I don't remember Hoplites' morale, but I think it's 10 or 11. At morale ten, the change to not be affected by the awe would be 54% (row 0+), and at morale eleven, change would be 62% (-1+). The 54% is quite close to the 50% member of the Illwinter said on the forum once.
Reverse-Cumulative Difference Statistics:
-10+: 96.554%
-9+: 95.373%
-8+: 93.822%
-7+: 91.805%
-6+: 89.194%
-5+: 85.852%
-4+: 81.605%
-3+: 76.281%
-2+: 69.830%
-1+: 62.391%
0+: 54.222%
1+: 45.773%
2+: 37.605%
3+: 30.165%
4+: 23.714%
5+: 18.388%
6+: 14.145%
7+: 10.802%
8+: 8.191%
9+: 6.174%
10+: 4.624%