Moldova has had a Russian backed separatist region called Transnistria since 1990. Moldova has had a hard time, they do not have huge resources they can use, and their military is not well- equipped or funded.

During the Soviet era the country was producing huge amounts of agricultural products. After dissolution, Moldova still relied heavily on export to Russia. It was mostly in their best interest to keep their heads down and carry on, as they do not have the means to fight a serious conflict.

They've also had massive brain drain. Large volumes of young people have been leaving the country for decades. Many young people with Romanian heritage applied to become Romanian-EU citizens when Romania joined the EU.

They have slowly been pivoting towards a pro-EU policy. Whenever they make an obvious plan to head more towards becoming European, Russia will often apply some kind of sanctions. It's been a common tactic over the last few decades for shipments of wine, cognac or other Moldovan products to be seized and 'destroyed' by Russian customs officials in retaliation for Pro-EU policy shifts by Moldova.

When the Preisdent of Belarus, Lukashenko, leaked Russia's Ukrainian invasion plans, Moldova was shown as being a point of troop movement. So Russias invasion plan definitely originally included Moldovan territory as well.