A User’s Guide to ROME II GRAND CAMPAIGN POLITICS - Part 9: Assassinate Wife, Divorce, Bribe, Adopt and Marriage

Assassinate Wife
This is the only political action that does not actually grant any directly political outcomes and only the ruling party's members can be targeted. The higher the character's Gravitas, the higher the financial cost to arrange the killing of his wife. Its only other side-effect is to remove the household trait provided by the character’s wife, freeing up the slot for a potential new one.
 Divorce
Same as Assassinate Wife except it has no financial cost and high political cost. Carrying out this action means losing the support of a good few more patricians than if you had just assassinated her. It also has a small negative effect on the targeted character’s Gravitas.
Bribe
Has the simple effect of removing a character from an opposition party and placing him in your own at a financial and a political cost. Useful if you need to decrease the amount of Gravitas within an opposition party and increase your own in order to readdress the balance. If successful, the bribed character will lose some of his Gravitas when he moves over. The financial cost is more for high-Gravitas characters.
Adopt
Same as Bribe except the target will not lose Gravitas when he moves over to your party. Note that party leaders cannot be adopted or bribed.
Marriage
This is the most effective of all the actions aimed at achieving better balance between the parties, but is also the most expensive, coming at a high political and financial cost. Arranging a marriage between the targeted character and one of your distant relatives instantly readdresses the Influence levels of the two involved parties, bringing them into better harmony. Only unmarried members of opposition parties can be targeted.

User’s Guide to ROME II GRAND CAMPAIGN POLITICS - Part 8: Assassinate

This is the most self-explanatory of all the actions and has the most obvious effect – it outright removes certain characters from the game. Killing a troublesome member of your own faction is no small matter, so it comes with a considerable financial cost, alongside a small political cost. Troublesome could mean an ambitious character with high Gravitas who is upsetting the balance of Influence, by causing his party to attain excessive support. Rather conveniently, one of your own party’s commanders or statesmen can also be marked for death, with your faction leader being the only exception. Characters with higher Gravitas are harder to eliminate, so have a much higher cost. Also note that it is not possible to completely destroy a political party by killing off all of their members – the party will always remain regardless. Additionally, as turns are ended new statesmen will always spawn into their party to represent them.

A User’s Guide to ROME II GRAND CAMPAIGN POLITICS - Part 7: Secure Promotion

Securing promotion can only be done with members of your own ruling party and its effects are not entirely political. What it actually does is give the target a higher civil status in political office. In doing so, it gives an immediate boost to his Gravitas. Such promotions also bestow characters with various different Cursus Honorum traits, which in turn provide different civil or military buffs. This action can be carried out multiple times up to a maximum level - as long as the target character is the right age and rank required for each successive promotion.  At the first level, the cost is the support of a few patricians. With each promotion after, there is an ascending financial cost in addition to losing that support.

A User’s Guide to ROME II GRAND CAMPAIGN POLITICS - Part 6: Political Actions

Maintaining stability is about making sure the total levels of Gravitas are at comparable levels between the parties in your faction. In order to help achieve or maintain this balance, the player can use the various political actions available to them, most of which incur a financial and/or a political cost. The political cost will always be loss of support from a few individuals in your patrician class, which in turn immediately affects your share of Influence. But remember that these actions can affect party Influence levels in the long term; if your attempts to manipulate Gravitas are successful, you will see more favourable changes as successive turns are ended.
To start with, clicking on a character’s portrait in the faction summary screen brings up the buttons used to carry out these actions, the costs of which are displayed on the respective tool-tips produced by each of them. Not all characters can be targeted with all actions; only the valid actions will be displayed for each of them.

A User’s Guide to ROME II GRAND CAMPAIGN POLITICS - Part 5: Influence and Support

As we've seen, Influence is shared out amongst the political parties in percentages displayed on the faction summary screen. These percentages correlate with how much support each party has from within their own faction, usually from an invisible patrician class. These are individuals such as senators, tribal elders, court nobles, and so on. The type of individual will vary depending on the culture of the faction being played (for example, the support given to the parties of the democratic Hellenistic factions comes from their citizens and not from a patrician class). In any case, there are always a limited number of these power-granting individuals, and they can only give their support to one party at any one time. Therefore, losing or gaining their support means a loss or gain of political Influence. This is important when deciding whether or not to carry out political actions, as many of them will cost the support of a fixed number of patricians in the short term.
You can observe exactly how many of these individuals support your party at the top of your faction summary screen. The displayed Influence percentages for the opposition parties also produce a tool-tip when your mouse is hovered over it, which details exactly how many individuals support them.

A User’s Guide to ROME II GRAND CAMPAIGN POLITICS - Part 4: Generals, Admirals, and Statesmen

You may have also noticed that the list of characters on the faction summary screen is not only populated by your generals and admirals (commanders) serving you in the field, but also statesmen back home in your capital. In political terms, statesmen are the same as commanders and have Influence-contributing Gravitas, but unlike commanders they don’t have a presence on the campaign map. They hold positions in office until a newly raised force is given to them or until a new army or navy is raised and needs leadership. Additionally, a commander does not have to die to be replaced; you can replace him by selecting his army on the campaign map and navigating to the replace option in the ‘General’s Details’ tab. If you choose to put an existing statesman in a position of command over an existing military or naval force, a swap in roles will occur and the previous commander of that force will be removed from the field, becoming a statesman himself.
Recruiting an existing statesman into a military or naval leadership role has no financial cost. However, the candidate pool of potential commanders will frequently be populated with previously inexistent characters that do have a financial cost to recruit. This cost is not only for the creation of a new military or naval commander, but essentially also represents the cost of bringing characters out of civilian life and into political reckoning. Rather importantly, they will already have predefined allegiances towards certain parties and once recruited, they will appear on the faction screen to contribute their own Gravitas to their party’s Influence.
The main thing to remember is that both commanders and statesmen alike will always remain in party politics until their deaths, regardless of their presence in the field. The notable difference between them in the political arena is that the generals and admirals have the added advantage of being able to actively increase their own Gravitas by winning battles. This could be one possible reason why you might want to replace an existing commander with another – in order to help boost the Gravitas of a politically inferior statesman by giving him the opportunity to attain some military victories. 
Many decisions to hire and fire commanders are choices with potential political ramifications, but it is often the case that circumstances will not make the choice so straightforward. For example, picture a scenario in which you are late in your campaign with a large and ever-expanding empire contributing to a high Imperium level. You are embroiled in a tough war, battling it out with another faction at the other side of the map, far from your faction capital. One of your top generals is killed in battle and you need to get another one out into the field as soon as possible to sustain your war efforts. But the next-best character – potentially the highest ranked commander in the candidate pool – is an existing statesman representing an opposition party. He is an ambitious character with high Gravitas; appointing him and giving him a chance at amassing more glory will possibly give his party greater Influence. It has the potential to drastically affect the balance, which is dangerously skewed against you. A civil war as a result of your waning political support is a real risk, and you are far from home where a coup d’état may take place. But you need good generals, so what choice do you make?
In reality, political actions could be used in multiple ways to get around this scenario, but this is just one minor example of a gameplay decision that can have some long-term political ramifications that might not be immediately obvious.

A User’s Guide to ROME II GRAND CAMPAIGN POLITICS - Part 3: Gravitas and Ambition

Gravitas is a character’s popularity and standing in the Roman world and is the key factor in determining their party's share of Influence. All the characters in a party contribute, but the effect is relative to the total Gravitas within other parties. So if an opposition party has several high-Gravitas members and you don't, the likelihood is that their Influence will increase as turns are ended, while yours will decrease.
Another thing to remember is that the Ambition of a character can increase the effect their Gravitas has on their party’s Influence, so it is prudent to be aware of how ambitious your generals are. The more ambitious a character is in relation to others, the more effect his Gravitas will have towards his party’s share of power.
To manipulate a party's share of Influence is to reduce or increase the amounts of Gravitas their characters possess. For example, one could attempt to discredit a party by spreading rumours about some or all of its members, reducing their overall Gravitas. Assassination of a prominent opposition member is another handy option that could have an even greater effect, since the entirety of one character’s contributing Gravitas can be removed completely in one swift action. Conversely, adoption steals a character into your own party, taking Gravitas away from one party and adding it to your own. More details will be given about political actions later on.