If their forces were not involved, then who is to blame?...是什么意思？

If their forces were not involved, then who is to blame?...

如果他们的部队没有介入，那么谁应该承担责任？

if

conj. 如果，倘若，即使，〈口〉是否，假设；n. 条件，设想；

例句
She was old enough to absent herself from the lunch table if she chose...
她长大了，可以自己做主不来吃午餐了。

their

pron. 他（她，它）们的，在提及性别不详的人时，用以代替 him 或 her；

例句
Their permissiveness toward their children reflects the wild abandon of their own lives.
他们对孩子的放任折射出他们自身生活的放浪形骸。

forces

n. 力( force的名词复数 )，武力，（社会）势力，气力；v. 强制( force的第三人称单数 )，强作，施强力于，促成早熟；

例句
Reports from Chad suggest that rebel forces are advancing on the capital...
来自乍得的报告显示叛军正向首都推进。

were

be的过去时复数和第二人称单数形式，有时代替 was,用于条件从句、动词 wish 之后等；

例句
Shops, houses, and vehicles were set ablaze.
店铺、房子和车辆全都陷于火海。

not

adv. 不，[用以表示否定、否认、拒绝、禁止等]不是，几乎不，未必，没有[用于否定后面的词或短语]；

例句
It became very clear that the incident was not just an aberration, it was not just a single incident.
事实已经很清楚，这件事不是偶发的，它并不是一起孤立的事件。

involved

adj. 复杂难懂的，与他人有密切关系的，受牵扯的，作为一部份参与的；v. 表明（某人参与了罪行等）(involve的过去式和过去分词)，使参与，牵涉，使专心于；

例句
She was involved in a serious car accident last week...
上星期她卷入了一场严重的车祸。

then

adv. 那时，然后，那么，话说回来；adj. 当时的，那时的；

例句
Liz adjusted her mirror and then edged the car out of its parking bay.
莉兹调了调后视镜，将车子挪出了停车位。

who

pron. 谁，什么人，关系代词，有先行词，孰；

例句
The last French king was Louis Philippe, who abdicated in 1848.
法国末代国王是1848年逊位的路易·菲力普。

is

vt.& vi. 是（be的三单形式；n. 存在；

例句
Bollinger 'RD' is a rare, highly prized wine.
博林格RD香槟是一种名贵的备受推崇的葡萄酒。

to

prep. 向，朝着，到，关于，属于；adv. 朝一个方向的，到某种状态，关闭；

例句
I suggest you leave it to an expert...
我建议你把它留给专家来解决。

blame

vt. 指责，责怪，归咎于；n. 责备，责任，过失；

例句
Eleanor would later blame her mother-in-law for her husband's frequent absences.
埃莉诺过后会因丈夫经常不在家而责怪婆婆。